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Question 1
B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
55%
(hard)
Question Stats:
58% (03:24) correct
42%
(03:20) wrong
based on 6299
sessions
History
Date
Time
Result
Not Attempted Yet
Question 2
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
84% (01:13) correct 16%
(01:26) wrong
based on 6878
sessions
History
Date
Time
Result
Not Attempted Yet
Question 3
D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
88% (00:48) correct 12%
(01:04) wrong
based on 6842
sessions
History
Date
Time
Result
Not Attempted Yet
Question 4
A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
35%
(medium)
Question Stats:
63% (01:11) correct 37%
(01:36) wrong
based on 6834
sessions
History
Date
Time
Result
Not Attempted Yet
Question 5
A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
70% (01:06) correct 30%
(01:16) wrong
based on 6644
sessions
History
Date
Time
Result
Not Attempted Yet
Question 6
D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
75%
(hard)
Question Stats:
45% (01:44) correct 55%
(01:45) wrong
based on 6449
sessions
History
Date
Time
Result
Not Attempted Yet
Question 7
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
85%
(hard)
Question Stats:
41% (01:38) correct 59%
(01:41) wrong
based on 6216
sessions
History
Date
Time
Result
Not Attempted Yet
Question 8
E
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
35%
(medium)
Question Stats:
64% (01:09) correct 36%
(01:18) wrong
based on 5812
sessions
History
Date
Time
Result
Not Attempted Yet
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.
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.
This question asks you to identify the primary focus of the passage. The best answer is the second choice. The author describes the new theoretical model in the first paragraph; in the final paragraph the author states that the data obtained from actual observations, which are discussed in the second and third paragraphs, is consistent with the new theoretical model.
The first choice is not correct; the computer model confirmed the astronomers' hypothesis that meteor streams broaden with time.
The third choice is also incorrect. Although the model yielded an unexpected result, the passage makes no reference to further areas for research.
The fourth choice incorrectly mentions two natural phenomena. Although the passage does mention two natural phenomena—a meteor stream and planetary gravitation—it focuses on only a single phenomenon, the meteor stream; there is mention that meteor streams are affected by planetary gravitation, but there is no explanation of how they relate, nor any demonstration of how to measure the phenomena themselves.
The last choice is not correct because it reverses the order of events. The model yielded a prediction that was subsequently confirmed by observational data; the model was not constructed to explain the data.
The first choice is not correct; the computer model confirmed the astronomers' hypothesis that meteor streams broaden with time.
The third choice is also incorrect. Although the model yielded an unexpected result, the passage makes no reference to further areas for research.
The fourth choice incorrectly mentions two natural phenomena. Although the passage does mention two natural phenomena—a meteor stream and planetary gravitation—it focuses on only a single phenomenon, the meteor stream; there is mention that meteor streams are affected by planetary gravitation, but there is no explanation of how they relate, nor any demonstration of how to measure the phenomena themselves.
The last choice is not correct because it reverses the order of events. The model yielded a prediction that was subsequently confirmed by observational data; the model was not constructed to explain the data.
(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
2. 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.
(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.
3. 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
(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
4. 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.
(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.
5. 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.
(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.
6. 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.
(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.
7. 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.
(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.
8. 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.
(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.
14 Aug 2015, 22:20
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8. Which of the following is an assumption underlying the last sentence of the passage?
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!
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!
Edith Wu
The point is not the length of the meteor shower but its thickness. The conventional theory says the distribution of particles would be increasingly dense toward the center of a meteor stream. So if Earth passes through a meteor stream, the density of particles will increase till Earth reaches the centre of the stream and then the density will start reducing again. Look at the diagram below:
Attachment:
QUA-orbit.png [ 42.77 KiB | Viewed 91213 times ]
Explained here:
Question 1: https://gmatclub.com/forum/a-meteor-str ... l#p3318420
Question 3: https://gmatclub.com/forum/a-meteor-str ... l#p3318426
Question 6: https://gmatclub.com/forum/a-meteor-str ... l#p2571607
