GMAT申友阅读RC题库-The author of the passage mentions “escape velocity” (see line 22) in order to help explain which of the following-OG2022-真题答案解析

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When asteroids collide, some collisions cause an asteroid to spin faster; others slow it down. If

asteroids are all monoliths—single rocks—undergoing random collisions, a graph of their rotation rates

should show a bell-shaped distribution with statistical “tails” of very fast and very slow rotators. If asteroids are rubble piles, however, the tail representing the very fast rotators would be missing, because any

loose aggregate spinning faster than once every few hours (depending on the asteroid’s bulk density)

would fly apart. Researchers have discovered that all but five observed asteroids obey a strict limit on rate of rotation. The exceptions are all smaller than 200 meters in diameter, with an abrupt cutoff for asteroids larger than that.

The evident conclusion—that asteroids larger than 200 meters across are multicomponent structures or rubble piles—agrees with recent computer modeling of collisions, which also finds a transition at that

diameter. A collision can blast a large asteroid to bits, but after the collision those bits will usually move

slower than their mutual escape velocity. Over several hours, gravity will reassemble all but the fastest pieces into a rubble pile. Because collisions among asteroids are relatively frequent, most large bodies have already suffered this fate. Conversely, most

small asteroids should be monolithic, because impact fragments easily escape their feeble gravity.

The author of the passage mentions “escape velocity” (see line 22) in order to help explain which of the following

A. The tendency for asteroids to become smaller rather than larger over time

B. The speed with which impact fragments reassemble when they do not escape an asteroid’s gravitational attraction after a collision

C. The frequency with which collisions among asteroids occur

D. The rotation rates of asteroids smaller than 200 meters in diameter

E. The tendency for large asteroids to persist after collisions

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Evaluation<

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This question asks about the purpose of the author’s use of the phrase escape velocity in the second paragraph. The author is discussing what occurs after an asteroid collision, in

which a large asteroid might be blasted to bits. The bits, according to the author, will move slower than their mutual escape velocity—that is, the speed at which they would have to move to get away from each other and not reassemble, under the influence of gravity, into a rubble pile.

A. The author is emphasizing the asteroid bits that do not escape rather than those that do. Asteroids may become smaller over time, but the fact that most bits move slower than their escape velocity would not help to explain this shrinkage.

B. That the bits of asteroid move slower than their escape velocity helps explain why the fragments reassemble, but it does not help explain the speed with which they

reassemble.

C. According to the author, asteroid collisions occur frequently, but the escape velocity of the resulting fragments does not help to explain that frequency.

D. The concept of escape velocity may help explain why small asteroids are monoliths, but it has no relevance, at least as far as the passage indicates, to those asteroids’ rotation

rates.

E. Correct. After a collision, it is the asteroid fragments’ failure to reach escape velocity that allows the fragments’ gravitational pull to reassemble them into a rubble pile.