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A meteor stream is composed of dust particles that have been

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A meteor stream is composed of dust particles that have been  [#permalink]

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New post Updated on: 13 Oct 2018, 02:11
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A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' individual orbits are perturbed by planetary gravitational fields. A recent computer-modeling experiment tested this hypothesis by tracking the influence of planetary gravitation over a projected 5,000-year period on the positions of a group of hypothetical dust particles. In the model, the particles were randomly distributed throughout a computer simulation of the orbit of an actual meteor stream, the Geminid. The researcher found, as expected, that the computer-model stream broadened with time. Conventional theories, however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream. Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.

Whenever the Earth passes through a meteor stream, a meteor shower occurs. Moving at a little over 1,500,000 miles per day around its orbit, the Earth would take, on average, just over a day to cross the hollow, computer-model Geminid stream if the stream were 5,000 years old. Two brief periods of peak meteor activity during the shower would be observed, one as the Earth entered the thick-walled "pipe" and one as it exited. There is no reason why the Earth should always pass through the stream's exact center, so the time interval between the two bursts of activity would vary from one year to the next.

Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.
The primary focus of the passage is on which of the following?
(A) Comparing two scientific theories and contrasting the predictions that each would make concerning a natural phenomenon
(B) Describing a new theoretical model and noting that it explains the nature of observations made of a particular natural phenomenon
(C) Evaluating the results of a particular scientific experiment and suggesting further areas for research
(D) Explaining how two different natural phenomena are related and demonstrating a way to measure them
(E) Analyzing recent data derived from observations of an actual phenomenon and constructing a model to explain the data


According to the passage, which of the following is an accurate statement concerning meteor streams?
(A) Meteor streams and comets start out with similar orbits, but only those of meteor streams are perturbed by planetary gravitation.
(B) Meteor streams grow as dust particles are attracted by the gravitational fields of comets.
(C) Meteor streams are composed of dust particles derived from comets.
(D) Comets may be composed of several kinds of materials, while meteor streams consist only of large dust particles.
(E) Once formed, meteor streams hasten the further disintegration of comets.


The author states that the research described in the first paragraph was undertaken in order to
(A) determine the age of an actual meteor stream
(B) identify the various structural features of meteor streams
(C) explore the nature of a particularly interesting meteor stream
(D) test the hypothesis that meteor streams become broader as they age
(E) show that a computer model could help in explaining actual astronomical data


Q. It can be inferred from the passage that which of the following would most probably be observed during the Earth's passage through a meteor stream if the conventional theories mentioned in line 18 were correct?
(A) Meteor activity would gradually increase to a single, intense peak, and then gradually decline.
(B) Meteor activity would be steady throughout the period of the meteor shower.
(C) Meteor activity would rise to a peak at the beginning and at the end of the meteor shower.
(D) Random bursts of very high meteor activity would be interspersed with periods of very little activity.
(E) In years in which the Earth passed through only the outer areas of a meteor stream, meteor activity would be absent.


According to the passage, why do the dust particles in a meteor stream eventually surround a comet’s original orbit?
(A) They are ejected by the comet at differing velocities.
(B) Their orbits are uncontrolled by planetary gravitational fields.
(C) They become part of the meteor stream at different times.
(D) Their velocity slows over time.
(E) Their ejection velocity is slower than that of the comet.


The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in line 18 and the new computer-derived theory?
(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the stream.
(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.
(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.
(D) Meteor showers caused by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.


It can be inferred from the last paragraph of the passage that which of the following must be true of the Earth as it orbits the Sun?
(A) Most meteor streams it encounters are more than 2,000 years old.
(B) When passing through a meteor stream, it usually passes near to the stream’s center.
(C) It crosses the Geminid meteor stream once every year.
(D) It usually takes over a day to cross the actual Geminid meteor stream.
(E) It accounts for most of the gravitational perturbation affecting the Geminid meteor stream.


Which of the following is an assumption underlying the last sentence of the passage?
(A) In each of the years between 1970 and 1979, the Earth took exactly 19 hours to cross the Geminid meteor stream.
(B) The comet associated with the Geminid meteor stream has totally disintegrated.
(C) The Geminid meteor stream should continue to exist for at least 5,000 years.
(D) The Geminid meteor stream has not broadened as rapidly as the conventional theories would have predicted.
(E) The computer-model Geminid meteor stream provides an accurate representation of the development of the actual Geminid stream.

OA:E




Please explain how to answer these questions.

Edit: Added missing questions.

Originally posted by pr90 on 13 Mar 2013, 07:46.
Last edited by workout on 13 Oct 2018, 02:11, edited 2 times in total.
Added timer for Q8
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Re: A meteor stream is composed of dust particles that have been  [#permalink]

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New post 14 Aug 2015, 22:20
5
It's safe to say that if you are thinking about the possible destruction of the Earth, you have strayed too far from the text! ;) As in a CR assumption question, we want something that bridges the conclusion at hand with other information provided directly in the passage.

One way to test our answers is to apply the Negation Test. If we negate the text in a particular answer choice and that poses a problem for the argument, then we have found a necessary assumption. If it doesn't, then we can cross that answer out. Let's try. First we need to keep in mind what conclusion we're dealing with. The last line says that the stream is about 3,000 years old. Why does the author think so? Because of the time it takes to get from one burst of meteor activity to the other. How can we connect the distance between the edges and the age of the stream? With the earlier information about the development of the stream over time. The conventional theories say that the stream should get dense in the center, while the computer model predicts a shape more like the hollow pipe. The observations in the last paragraph seem to match the computer model, so the author figures that we can use that model to determine how long the stream took to get this way. Now let's look at how each answer choices relates once we negate:

(A) The Earth did not take exactly 19 hours to cross each year. This is fine. In fact, the passage makes it clear that the time should vary from year to year. 19 hours is just an average. Eliminate.

(B) The comet has not totally disintegrated. Well, what do we mean by totally disintegrated? There are still chunks? What are we supposed to do with that information. Maybe some meteors are bigger than others and maybe they aren't. This doesn't connect to anything we know about the size, shape, or age of the stream.

(C) The stream should not continue to exist for 5,000 years. Okay, but what we want to look at what has already happened. Also, the fact that the computer model covers a 5,000-year period does not tell us how much longer a 3,000-year-old meteor stream should last.

(D) The stream has broadened as rapidly as the conventional theory predicted. This might seem to support the conventional theory and thereby pose a threat to the author's view. However, the distinction the author is making in the last paragraph between the two theories is not how fast the stream broadens, but whether it condenses or hollows out in the center.

(E) The computer model does NOT provide an accurate representation of the development of the actual Geminid system. If that were the case, then it wouldn't be safe to use the model to determine the age of the system, even if its prediction about the hollow center seemed correct. If the stream took a much longer or shorter time to spread out than that predicted by the computer model, then it would not be safe to conclude that the stream is about 3,000 years old. Answer choice (E) as originally worded is a necessary assumption.

I hope that helps!
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Re: A meteor stream is composed of dust particles that have been  [#permalink]

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New post 13 Mar 2013, 11:57
5
I changed the tag to 700 because this was really tough and comes from OG 11th edition

Q. It can be inferred from the passage that which of the
following would most probably be observed during
the Earth's passage through a meteor stream if the
conventional theories mentioned in line 18 were
correct?

(A) Meteor activity would gradually increase to a
single, intense peak, and then gradually decline.

This is stated in the passage "Conventional theories, however, predicted
that the distribution of particles would be
increasingly dense toward the center of a meteor
stream.


(B) Meteor activity would be steady throughout the
period of the meteor shower.

this contraddict A

(C) Meteor activity would rise to a peak at the
beginning and at the end of the meteor shower.

No is false

(D) Random bursts of very high meteor activity
would be interspersed with periods of very little
activity.

I didn't see anything about that

(E) In years in which the Earth passed through only
the outer areas of a meteor stream, meteor
activity would be absent.

I didn't see something about "absent"

The second one was even tough

The passage suggests that which of the following is a
prediction concerning meteor streams that can be
derived from both the conventional theories
mentioned in line 18 and the new computer-derived
theory?
(A) Dust particles in a meteor stream will usually be
distributed evenly throughout any cross section
of the stream.

Dust particles is not the poin of theories

(B) The orbits of most meteor streams should cross
the orbit of the Earth at some point and give rise
to a meteor shower.

neither the orbit

(C) Over time the distribution of dust in a meteor
stream will usually become denser at the outside
edges of the stream than at the center.

We know that is not true

D) Meteor showers caused by older meteor streams
should be, on average, longer in duration than those caused by very young meteor streams.

This is the line 8 " Astronomers have
hypothesized that a meteor stream should broaden
with time as the dust particles' individual orbits are
perturbed by planetary gravitational fields.
The older is the meteor, more broaden is its stream, viceversa is a younger comet


(E) The individual dust particles in older meteor
streams should be, on average, smaller than those
that compose younger meteor streams.

Average is not the point of this inference question
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Re: A meteor stream is composed of dust particles that have been  [#permalink]

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New post 16 Mar 2013, 06:36
carcass wrote:
I changed the tag to 700 because this was really tough and comes from OG 11th edition

Q. It can be inferred from the passage that which of the
following would most probably be observed during
the Earth's passage through a meteor stream if the
conventional theories mentioned in line 18 were
correct?

(A) Meteor activity would gradually increase to a
single, intense peak, and then gradually decline.

This is stated in the passage "Conventional theories, however, predicted
that the distribution of particles would be
increasingly dense toward the center of a meteor
stream.


(B) Meteor activity would be steady throughout the
period of the meteor shower.

this contraddict A

(C) Meteor activity would rise to a peak at the
beginning and at the end of the meteor shower.

No is false

(D) Random bursts of very high meteor activity
would be interspersed with periods of very little
activity.

I didn't see anything about that

(E) In years in which the Earth passed through only
the outer areas of a meteor stream, meteor
activity would be absent.

I didn't see something about "absent"

The second one was even tough

The passage suggests that which of the following is a
prediction concerning meteor streams that can be
derived from both the conventional theories
mentioned in line 18 and the new computer-derived
theory?
(A) Dust particles in a meteor stream will usually be
distributed evenly throughout any cross section
of the stream.

Dust particles is not the poin of theories

(B) The orbits of most meteor streams should cross
the orbit of the Earth at some point and give rise
to a meteor shower.

neither the orbit

(C) Over time the distribution of dust in a meteor
stream will usually become denser at the outside
edges of the stream than at the center.

We know that is not true

D) Meteor showers caused by older meteor streams
should be, on average, longer in duration than those caused by very young meteor streams.

This is the line 8 " Astronomers have
hypothesized that a meteor stream should broaden
with time as the dust particles' individual orbits are
perturbed by planetary gravitational fields.
The older is the meteor, more broaden is its stream, viceversa is a younger comet


(E) The individual dust particles in older meteor
streams should be, on average, smaller than those
that compose younger meteor streams.

Average is not the point of this inference question


Perfect explanation. Though i tried to apply my so called "Skimming techniques", i got both the answers wrong. Sometimes, you have to just read the passage in detail! Please do let me know if you followed any other technique to "read" the passage
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New post 16 Mar 2013, 07:39
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If you can distinguish what is the difference between the conventional and computer theory, job is done.
Conventional theories predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream.
Computer theory opposes the same and that is what passage is focusing on. This theory says that the concentration wont be dense but will broaden with time.

To answer both the question, this understanding is enough. I skimmed most of the parts of the passage and was able to get both right.
If we can understand what author is focusing on, job is done.
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Re: A meteor stream is composed of dust particles that have been  [#permalink]

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New post 27 Mar 2014, 09:07
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3
A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' individual orbits are perturbed by planetary gravitational fields. A recent computer-modeling experiment tested this hypothesis by tracking the influence of planetary gravitation over a projected 5,000-year period on the positions of a group of hypothetical dust particles. In the model,
the particles were randomly distributed throughout a computer simulation of the orbit of an actual meteor stream, the Geminid. The researcher found, as expected, that the computer-model stream broadened with time. Conventional theories, however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor
stream. Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.

Whenever the Earth passes through a meteor stream, a meteor shower occurs. Moving at a little over 1,500,000 miles per day around its orbit, the Earth would take, on average, just over a day to cross the hollow, computer-model Geminid stream if the stream were 5,000 years old. Two brief periods of peak meteor activity during the shower would be observed, one as the Earth entered the thick-walled "pipe" and one as it exited. There is no reason why the Earth should always pass through the stream's exact center, so the time interval between the two bursts of activity would vary from one year to the next.

Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. The time intervals between the bursts suggest the actual
Geminid stream is about 3,000 years old.


Q3: The author states that the research described in the first paragraph was undertaken in order to

(A) determine the age of an actual meteor stream
(B) Identify the various structural features of meteor streams
(C) explore the nature of a particularly interesting meteor stream
(D) test the hypothesis that meteor streams become broader as they age
(E) show that a computer model could help in explaining actual astronomical data

OA:


Explanation:
P1 middle -> Astronomers has hypothesized that a meteor stream should broaden with time..
-> experiment tested this hypothesis....


Q4: It can be inferred from the passage that which of the following would most probably be observed during the Earth’s passage through a meteor stream if the conventional theories mentioned in line 14 were

(A) Meteor activity would gradually increase to a single, intense peak, and then gradually decline.
(B) Meteor activity would be steady throughout the period of the meteor shower.
(C) Meteor activity would rise to a peak at the beginning and at the end of the meteor shower.
(D) Random bursts of very high meteor activity would be interspersed with periods of very little activity.
(E) In years in which the Earth passed through only the outer areas of a meteor stream, meteor activity would be absent.

OA:

OE:
increasingly dense towards the centre


Q5: According to the passage, why do the dust particles in a meteor stream eventually surround a comet’s orginla orbit?

(A) They are ejected by the comet at differing velocities.
(B) Their orbits are uncontrolled by planetary gravitational fields.
(C) They become part of the meteor stream at different times.
(D) Their velocity slows over time.
(E) Their ejection velocity is slower than that of the comet.

OA:

OE:
First sentence -> dust particles that have been ejected from a parent comet at a variety of velocities



Q6: The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in line 14 and the new computer-derived theory?

(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the steam.
(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.
(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.
(D) Meteor showers caused by older by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.

OA:

OE:
Both theories contend that meteor streams broaden over time.
Earth will experience longer showers with older stream, which is wider, than
the one with younger stream, which is narrower.


Q7: It can be inferred from the last paragraph of the passage that which of the following must be true of the Earth as it orbits the Sun?

(A) Most meteor streams it encounters are more than 2,000 years old.
(B) When passing through a meteor stream, it usually passes near to the stream’s center.
(C) It crosses the Geminid meteor stream once every year.
(D) It usually takes over a day to cross the actual Geminid meteor stream.
(E) It accounts of msot of the gravitaitonal perturbation affecting the Geminid meteor stream.

OA:


Q8: Which of the following is an assumption underlying the last sentence of the passage?

(A) In each of the years between 1970 and 1979, the Earth took exactly 19 hours to cross the Geminid meteor stream.
(B) The comet associated with the Geminid meteor stream has totally disintegrated.
(C) The Geminid meteor stream should continue to exist for at least 5,000 years.
(D) The Geminid meteor stream has not broadended as rapidly as the conventiona ltheories would have predicted.
(E) The computer-model Geminid meteor stream provides an accurate representation of the development of the
actual Geminid stream.

OA:

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Re: A meteor stream is composed of dust particles that have been  [#permalink]

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New post 24 Apr 2014, 12:01
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BangOn wrote:
If you can distinguish what is the difference between the conventional and computer theory, job is done.
Conventional theories predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream.
Computer theory opposes the same and that is what passage is focusing on. This theory says that the concentration wont be dense but will broaden with time.

To answer both the question, this understanding is enough. I skimmed most of the parts of the passage and was able to get both right.
If we can understand what author is focusing on, job is done.


this one was tricky, i guess you need to practice enough to tackle such RC (specially when you are from law field ) . Practice Practice Parctice
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Re: A meteor stream is composed of dust particles that have been  [#permalink]

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New post 02 May 2014, 13:50
The second one stumped me and I ended up choosing "B" when it was indeed "D". It was always a toss up between B and D, and I incorrectly assumed B to be a milder (and hence more plausible) answer. I missed the "orbit" portion.

Thanks for sharing this question!
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New post 29 Jan 2015, 06:57
Q7: It can be inferred from the last paragraph of the passage that which of the following must be true of the Earth as it orbits the Sun?

(C) It crosses the Geminid meteor stream once every year.

I don't really understand. Where does it state anything about crossing a stream once every year?
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New post 01 Feb 2015, 00:20
Combine the first sentence of paragraph 3 with the first sentence of paragraph 2. P3 tells us there is an annual Geminid meteor shower. P2 tells us that meteor showers occur when we pass through a meteor stream. It's pretty common that even when they ask you to infer from one part of the passage, you have to use what you've learned elsewhere in the passage to interpret that information.

Hope that helps!
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New post 01 Feb 2015, 10:24
5/6 correct : Completed in 12 min. 30 sec

Question 4 : Why is C not correct?

Can any one pls explain a bit more.
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New post 01 Feb 2015, 11:30
In Q4, C matches what would happen if we were working with the distribution seen in the computer model--"a thick-walled, hollow pipe." Passing through that, we'd get a burst of activity, then a break (while we're in the "hollow" part) and then another burst. However, this computer model was a surprising deviation from conventional theories, which held that the distribution would be increasingly dense toward the center. Travelling through that, we'd expect activity to increase until we hit the peak and then taper off again.
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New post 06 May 2015, 01:33
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elenaekenger wrote:
Q7: It can be inferred from the last paragraph of the passage that which of the following must be true of the Earth as it orbits the Sun?

(C) It crosses the Geminid meteor stream once every year.

I don't really understand. Where does it state anything about crossing a stream once every year?

As Dmitry has correctly mentioned, the following line from the passage basically gives this information: Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower?

So, the presence of "yearly" is the most strong indicator that Earth crosses the Geminid meteor stream once every year.

Quite tricky though; had to really strain my eyes.
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New post 29 Jul 2015, 15:05
goodyear2013 wrote:
A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' individual orbits are perturbed by planetary gravitational fields. A recent computer-modeling experiment tested this hypothesis by tracking the influence of planetary gravitation over a projected 5,000-year period on the positions of a group of hypothetical dust particles. In the model, the particles were randomly distributed throughout a computer simulation of the orbit of an actual meteor stream, the Geminid. The researcher found, as expected, that the computer-model stream broadened with time. Conventional theories, however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream. Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.

Whenever the Earth passes through a meteor stream, a meteor shower occurs. Moving at a little over 1,500,000 miles per day around its orbit, the Earth would take, on average, just over a day to cross the hollow, computer-model Geminid stream if the stream were 5,000 years old. Two brief periods of peak meteor activity during the shower would be observed, one as the Earth entered the thick-walled "pipe" and one as it exited. There is no reason why the Earth should always pass through the stream's exact center, so the time interval between the two bursts of activity would vary from one year to the next.

Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.

Q5: According to the passage, why do the dust particles in a meteor stream eventually surround a comet’s original orbit?

(A) They are ejected by the comet at differing velocities.
(B) Their orbits are uncontrolled by planetary gravitational fields.
(C) They become part of the meteor stream at different times.
(D) Their velocity slows over time.
(E) Their ejection velocity is slower than that of the comet.

OA:

OE:
First sentence -> dust particles that have been ejected from a parent comet at a variety of velocities



I was confused by this one. In the passage, it states that "A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities." I bolded the word parent because that implies the parent comet referenced and the comet the dust particles surround are two different comets. Thus, when the question asks about the comet that dust particles have surrounded, they are ejected by the "parent" comet, and not the comet that the dust particles surround. What am I missing? Why do they even bother to include the word "parent"? To trick out overthinkers like me?
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New post 29 Jul 2015, 22:48
Can anyone explain Q6? ... Where does it say that the conventional theory contends that meteor stream broadens over time?
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New post 29 Jul 2015, 23:12
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There are two references to this:

1) "Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' individual orbits are perturbed by planetary gravitational fields."

2) "The researcher found, as expected, that the computer-model stream broadened with time."

The first item is introducing an earlier idea ("conventional theory") that was validated by the computer model in the second item.

For a detailed analysis, check out our blog:

https://www.manhattanprep.com/gmat/blog ... m-passage/
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New post 03 Aug 2015, 07:48
can sum1 explain q6...i know that they hav mentioned yearly word..but v r questioning abt that n not answering..
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New post 11 Aug 2015, 14:12
DmitryFarber wrote:
There are two references to this:

1) "Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' individual orbits are perturbed by planetary gravitational fields."

2) "The researcher found, as expected, that the computer-model stream broadened with time."

The first item is introducing an earlier idea ("conventional theory") that was validated by the computer model in the second item.

For a detailed analysis, check out our blog:

https://www.manhattanprep.com/gmat/blog ... m-passage/


Hi Dmitry, Could you please explain question 8. I chose B , because if the comet existed then we may not have only 2 peak intervals but more and also the earth would be destroyed. In my opinion the last para does not state that the data used in 1970 to 1979 was from the model and not actually observed. Nor is it mentioned that to measure the time intervals we only use the computer model.

Please help me !!

Thanks and kudos !
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New post 15 Aug 2015, 05:56
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DmitryFarber wrote:
It's safe to say that if you are thinking about the possible destruction of the Earth, you have strayed too far from the text! ;) As in a CR assumption question, we want something that bridges the conclusion at hand with other information provided directly in the passage.

One way to test our answers is to apply the Negation Test. If we negate the text in a particular answer choice and that poses a problem for the argument, then we have found a necessary assumption. If it doesn't, then we can cross that answer out. Let's try. First we need to keep in mind what conclusion we're dealing with. The last line says that the stream is about 3,000 years old. Why does the author think so? Because of the time it takes to get from one burst of meteor activity to the other. How can we connect the distance between the edges and the age of the stream? With the earlier information about the development of the stream over time. The conventional theories say that the stream should get dense in the center, while the computer model predicts a shape more like the hollow pipe. The observations in the last paragraph seem to match the computer model, so the author figures that we can use that model to determine how long the stream took to get this way. Now let's look at how each answer choices relates once we negate:

(A) The Earth did not take exactly 19 hours to cross each year. This is fine. In fact, the passage makes it clear that the time should vary from year to year. 19 hours is just an average. Eliminate.

(B) The comet has not totally disintegrated. Well, what do we mean by totally disintegrated? There are still chunks? What are we supposed to do with that information. Maybe some meteors are bigger than others and maybe they aren't. This doesn't connect to anything we know about the size, shape, or age of the stream.

(C) The stream should not continue to exist for 5,000 years. Okay, but what we want to look at what has already happened. Also, the fact that the computer model covers a 5,000-year period does not tell us how much longer a 3,000-year-old meteor stream should last.

(D) The stream has broadened as rapidly as the conventional theory predicted. This might seem to support the conventional theory and thereby pose a threat to the author's view. However, the distinction the author is making in the last paragraph between the two theories is not how fast the stream broadens, but whether it condenses or hollows out in the center.

(E) The computer model does NOT provide an accurate representation of the development of the actual Geminid system. If that were the case, then it wouldn't be safe to use the model to determine the age of the system, even if its prediction about the hollow center seemed correct. If the stream took a much longer or shorter time to spread out than that predicted by the computer model, then it would not be safe to conclude that the stream is about 3,000 years old. Answer choice (E) as originally worded is a necessary assumption.

I hope that helps!


Thank you so much for such a detailed analysis and explanation.
As you have pointed out Option B is not connecting the dots. In my mind Option E is the clear answer now.

Thanks again and kudos !!
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Re: A meteor stream is composed of dust particles that have been &nbs [#permalink] 15 Aug 2015, 05:56

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