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GMAT RC – When asteroids collide, some collisions cause an asteroid to spin

Passage

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.

Questions

Question 1. The passage implies which of the following about the five asteroids mentioned in line 12?

A. Their rotation rates are approximately the same.
B. They have undergone approximately the same number of collisions.
C. They are monoliths.
D. They are composed of fragments that have escaped the gravity of larger asteroids.
E. They were detected only recently.

Question 2. The discovery of which of the following would call into question the conclusion mentioned in line 16 [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. An asteroid 100 meters in diameter rotating at a rate of once per week
B. An asteroid 150 meters in diameter rotating at a rate of 20 times per hour
C. An asteroid 250 meters in diameter rotating at a rate of once per week
D. An asteroid 500 meters in diameter rotating at a rate of once per hour
E. An asteroid 1,000 meters in diameter rotating at a rate of once every 24 hours

Question 3. According to the passage, which of the following is a prediction that is based on the strength of the gravitational attraction of small asteroids?

A. Small asteroids will be few in number.
B. Small asteroids will be monoliths.
C. Small asteroids will collide with other asteroids very rarely.
D. Most small asteroids will have very fast rotation rates.
E. Almost no small asteroids will have very slow rotation rates.

Question 4. 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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