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Before the age of space exploration, the size and composition of the m

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Before the age of space exploration, the size and composition of the m [#permalink]

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New post 07 Jun 2013, 14:20
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Question 1
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C
D
E

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57% (02:03) correct 43% (01:52) wrong based on 175

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C
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E

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58% (00:30) correct 42% (00:29) wrong based on 157

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C
D
E

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41% (00:33) correct 59% (00:36) wrong based on 150

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53% (00:34) correct 47% (00:26) wrong based on 59

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Before the age of space exploration, the size and composition of the moon's core were astronomical mysteries. Astronomers assumed that the moon's core was smaller than that of the Earth, in both relative and absolute terms — the radius of the Earth's core is 55 percent of the overall radius of the Earth and the core's mass is 32 percent of the Earth's overall mass — but they had no way to verify their assumption. However, data gathered by Lunar Prospector have now given astronomers the ability to determine that the moon's core accounts for 20 percent of the moon's radius and for a mere 2 percent of its overall mass.

The data have been used in two ways. In the first method, scientists measured minute variations in radio signals from Lunar Prospector as the craft moved towards or away from the Earth. These variations allowed scientists to detect even the slightest changes in the craft's velocity while the craft orbited the moon. These changes resulted from inconsistency in the gravitational pull of the moon on the craft, and permitted scientists to create a "gravity map" of both near and far sides of the moon. This map, in turn, revealed to scientists the distribution of the moon's internal mass. Scientists were then able to determine that the moon has a small, metallic core, which, if composed mostly of iron, has a radius of approximately 350 kilometers. The second method involved examining the faint magnetic field generated within the moon itself by the moon's monthly passage through the tail of the Earth's magnetosphere. This approach confirmed the results obtained through examination of the gravity map.

The size and composition of the moon's core are not academic concerns; they have serious implications for our understanding of the moon's origins. For example, if the moon and Earth developed as distinct entities, the sizes of their cores should be more comparable. In actuality, it seems that the moon was once part of the Earth and broke away at an early stage in the Earth's evolution, perhaps as the result of a major asteroid impact. The impact could have loosened iron that had not already sunk to the core of the Earth, allowing it to form the core around which the moon eventually coalesced. Alternatively, according to fission theory, the early Earth may have spun so rapidly that it ejected a quantity of material by so-called centrifugal force, material that later coalesced by mutual gravitational attraction into the Moon.

[Reveal] Spoiler:
D

1. The primary purpose of the passage is best expressed as

(A) The author discusses the method of data utilization that proved that the moon was once part of the earth.

(B) The author discusses the methods of data utilization that changed scientists' opinions about the relative sizes of the earth's and moon's cores.

(C) The passage studies the method that, using data about radii and core mass, led to important implications about the origin of the planets.

(D) The passage studies the use of scientific methods to analyze data and confirm a hypothesis and references possible deductions.

(E) The passage discusses the implications following from the size of the Earth's core.


[Reveal] Spoiler:
D

2. According to the passage, scientists employed one research method that measured

(A) changes in a spacecraft's velocity as it returned to Earth

(B) changes in the gravitational pull on the Lunar Prospector as it orbited the moon

(C) changes in the moon's gravity as it orbited the earth

(D) changes in a spacecraft's radio signals as it changed position relative to the earth

(E) changes in the moon's gravitational pull over time



[Reveal] Spoiler:
C


3. The author mentioned “gravity map” in the second paragraph in order to

(A) illustrate the method used to correct the Lunar Prospector’s velocity

(B) confirm the results obtained by examining the moon’s magnetic field

(C) detail a step in the investigation of the composition of a specific orbiting

(D) detail a step in the investigation of the effects of gravity on the moon and earth

(E) explain a step in the process of confirming a new hypothesis and discarding an older theory


[Reveal] Spoiler:
A

4. It can be inferred from the passage that

(A) the earth’s core contributes a higher proportion of both the earth’s total radius and its total mass than the core of the moon contributes to its own total radius and mass

(B) a comparison of the earth’s and moon’s cores suggests that the earth did break away from the moon

(C) scientists will eventually be able to use the gravity map to further the proof that a major asteroid impact caused the earth and moon to separate

(D) because the earth and moon were once joined, it is probable that scientists will eventually discover fossils and other evidence on the moon that indicates that a major asteroid impact caused the extinction of the dinosaurs

(E) the moon’s core has a higher ratio of iron in its composition than does the earth’s


[Reveal] Spoiler:
B

5. According to the passage, the magnetic field within the Moon’s core

(A) confirms the inconsistencies in radio signal wavelength detected by the Lunar Prospector

(B) is produced when the Moon moves through the Earth’s magnetosphere

(C) calls the results of the radio signal analysis into question

(D) permits the creation of a gravity map corresponding to lunar mass concentrations

(E) indicates the speed and direction of travel of the Moon


[Reveal] Spoiler:
C

6. If the wavelength of radio signals emitted by the Lunar Prospector were constant, then which of the following could be most properly inferred?

(A) The velocity of the spacecraft depends on whether it is on the near or far side of the Moon.

(B) The size and mass of the Moon’s core may be more comparable to the size and mass of the Earth’s core than is currently believed.

(C) As the craft orbits the moon, the Moon exerts a constant gravitational pull on the craft.

(D) The Earth and the Moon seem to have originated independently.

(E) It would be impossible to create a gravity map of the Moon.


[Reveal] Spoiler:
E

7. In the last sentence of the passage, the author uses the word “so-called” primarily in order to imply that

(A) the force may not have been adequate to cause the claimed ejection

(B) fission theory may have less explanatory power than impact theory

(C) the later coalescence of the Moon’s material may not have occurred as a result of centrifugal force

(D) the speed of the early Earth’s rotation may have led to the creation of the Moon

(E) the phenomenon in question might more properly be re-named

[Reveal] Spoiler: Question #1 OA
[Reveal] Spoiler: Question #2 OA
[Reveal] Spoiler: Question #3 OA
[Reveal] Spoiler: Question #4 OA
[Reveal] Spoiler: Question #5 OA
[Reveal] Spoiler: Question #6 OA
[Reveal] Spoiler: Question #7 OA

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Last edited by hazelnut on 14 Nov 2017, 20:57, edited 4 times in total.
Added question 5, 6 & 7.

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Re: Before the age of space exploration, the size and composition of the m [#permalink]

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New post 09 Jun 2013, 23:17
My answers
1.D 2.E 3.C 4.B

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Re: Before the age of space exploration, the size and composition of the m [#permalink]

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New post 10 Jun 2013, 09:24

Kudos [?]: 9494 [0], given: 1203

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Re: Before the age of space exploration, the size and composition of the m [#permalink]

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New post 12 Jun 2013, 09:35
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1.
The passage first talks about astronomers' assumptions regarding the earth's and
moon's radii and core mass. The next two paragraphs detail the two methods
astronomers employed to analyze their assumptions by using data collected by
Lunar Prospector. The last paragraph discusses the implications of this data.
(A) This choice founders over the use of the singular word "method" and the word
"proved." There were two methods, and "proved" is too extreme.
(B) This choice uses the word "changed," which is factually wrong because the
passage says that it confirmed an assumption.
(C) This choice fails because of the use of the singular "method," and because
"planets" is too general for a passage only concerning the Earth and its moon.
(D) CORRECT. It is acceptable to equate "implications" and "deductions," as well as
"hypothesis" and "assumption."
(E) This choice ignores the entire passage except for the last paragraph, and thus by
definition can not be the passage's sum.

2.
The information to answer this question must come from the second or third
paragraph. As it turns out, the choices all relate to the second one. The second
sentence of that paragraph reads "measured minute variations in radio signals from
Lunar Prospector as the craft moved towards or away from the Earth."

(A) Changes in the craft's velocity were measured while the craft orbited the moon,
not as A states as the craft "returned to Earth."

(B) Although measurements of the Lunar Prospector 's velocity allowed scientists to
create a "gravity map," the scientists did not measure directly the gravitational pull on
the craft.

(C) This choice is incorrect because the passage does not discuss changes in the
moon's gravity.

(D) CORRECT. The phrase "changed position relative to the earth" is a fair
equivalent of "moved towards or away from the Earth."
(E) This choice is incorrect because the passage does not discuss changes in the
moon's gravitational pull over time.

3.
This question asks why the author included this detail. The "gravity map" was a step
in the determination of the size of the moon's core. We must find a choice that
reflects this.
(A) This choice is a distortion—the method was not used in this way.
(B) This choice not only comes from the third paragraph but also reverses the
relationship--the magnetic field work confirmed the map.
(C) CORRECT. The author put in the detail to show a step in the investigation of the
core ("composition") of the moon ("orbiting body").
(D) This choice contains the false word "earth"; in fact, the "moon" is the sole focus
of the investigation of gravity's effects.
(E) This choice incorrectly states that an older theory was discarded; in fact the old
assumption was confirmed.

4.
Because the question is open-ended, the best approach is to evaluate the choices.

(A) CORRECT. The information contained in A can be proven from the information in
the passage. The ratios that it discusses can be found in the first paragraph: the
earth's core contributes 55% of the earth's radius and 32% of its mass, compared to
the moon's core contributing 20% of the moon's radius and 2% of its mass. Like
many correct answers to inferences, the inference is very small.

(B) This choice reverses the relationship suggested in the passage--that the moon
might have broken away from the earth.

(C) This choice does not have to be true both because said proof is not certain and
because it is even less clear that the gravity map could be used for that purpose.

(D) This choice is a typical GMAT flight of fancy that sometimes is given as a wrong
choice; as dinosaurs are not mentioned at all, this answer is impossible.

(E) This choice does not have to follow from the information provided. The passage
does not give any information about the percentage of iron in the earth's core nor
does it compare that aspect of the two cores.
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Re: Before the age of space exploration, the size and composition of the m [#permalink]

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New post 14 Nov 2017, 20:59
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carcass wrote:
Before the age of space exploration, the size and composition of the moon's core were astronomical mysteries. Astronomers assumed that the moon's core was smaller than that of the Earth, in both relative and absolute terms — the radius of the Earth's core is 55 percent of the overall radius of the Earth and the core's mass is 32 percent of the Earth's overall mass — but they had no way to verify their assumption. However, data gathered by Lunar Prospector have now given astronomers the ability to determine that the moon's core accounts for 20 percent of the moon's radius and for a mere 2 percent of its overall mass.

The data have been used in two ways. In the first method, scientists measured minute variations in radio signals from Lunar Prospector as the craft moved towards or away from the Earth. These variations allowed scientists to detect even the slightest changes in the craft's velocity while the craft orbited the moon. These changes resulted from inconsistency in the gravitational pull of the moon on the craft, and permitted scientists to create a "gravity map" of both near and far sides of the moon. This map, in turn, revealed to scientists the distribution of the moon's internal mass. Scientists were then able to determine that the moon has a small, metallic core, which, if composed mostly of iron, has a radius of approximately 350 kilometers. The second method involved examining the faint magnetic field generated within the moon itself by the moon's monthly passage through the tail of the Earth's magnetosphere. This approach confirmed the results obtained through examination of the gravity map.

The size and composition of the moon's core are not academic concerns; they have serious implications for our understanding of the moon's origins. For example, if the moon and Earth developed as distinct entities, the sizes of their cores should be more comparable. In actuality, it seems that the moon was once part of the Earth and broke away at an early stage in the Earth's evolution, perhaps as the result of a major asteroid impact. The impact could have loosened iron that had not already sunk to the core of the Earth, allowing it to form the core around which the moon eventually coalesced. Alternatively, according to fission theory, the early Earth may have spun so rapidly that it ejected a quantity of material by so-called centrifugal force, material that later coalesced by mutual gravitational attraction into the Moon.
7. In the last sentence of the passage, the author uses the word “so-called” primarily in order to imply that

(A) the force may not have been adequate to cause the claimed ejection

(B) fission theory may have less explanatory power than impact theory

(C) the later coalescence of the Moon’s material may not have occurred as a result of centrifugal force

(D) the speed of the early Earth’s rotation may have led to the creation of the Moon

(E) the phenomenon in question might more properly be re-named



OFFICIAL EXPLANATION


The context in which the author uses “so-called” is this: “the early Earth may have been spinning so rapidly that it ejected a quantity of material by so-called centrifugal force…” We need only focus on the final phrase, “so-called centrifugal force.” With “so-called,” the author indicates that, while some call the phenomenon “centrifugal force,” there may be another, perhaps better name.

(A) The term “so-called” specifically modifies “centrifugal force,” not “ejected.” The term does not imply that the force was insufficiently strong to eject a quantity of material.

(B) The two theories are not contrasted through the use of this word.

(C) According to the passage, the material “coalesced by mutual gravitational attraction,” not centrifugal force. The ejection of the material apparently occurred by “so-called centrifugal force.”

(D) The theory does indicate that the speed of the Earth’s rotation may have led to the creation of the Moon, but the term “so-called” modifies only the term “centrifugal force.” It does not address the overall theory.

(E) CORRECT. The phenomenon in question is “centrifugal force” and the description “so-called” implies that the term centrifugal force might not be the most proper name or description of what is occurring.
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Re: Before the age of space exploration, the size and composition of the m   [#permalink] 14 Nov 2017, 20:59
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