When asteroids collide, some collisions cause an asteroid to spin fast

Hi suminha,

Let me know if this helps.

P1: The first para discusses about the asteroid collisions and that some collisions cause asteroid to spin faster, where as some slow it down. Asteroid can be classified in to 2 types: rubber piles, and monoliths. Rubber piles asteroids dont have a tail,so any loose end present that spins faster than once every few hours, flies apart. Researchers have discovered that all asteroids with a possible exception of 5 (smaller than 200 meters) obey strict rotation.

P2: Author mentions that there is evident conclusion that asteroids larger than 200 meters are multicomponent structures or rubble piles. Collisions can blast larger asteroids to smaller pieces and each of the smaller piece then move slower than their mutual escape velocity. Thus if the smaller pieces moved faster than their combined escape velocity, larger asteroid would blast, but of they move slower, it would not happen, as they would by reassmebled by gravity. Author concludes by stating that all small asteroids should be monolithics.


Thanks.

Thank you BM2201 !

It helped me to re-think this passage and found the problem of my process of thinking.

I think that this RC is especially hard, since it is tricky to identify Main Idea and Supporting Idea.
Normally I find two different objects that the author claims, and I contrast them and paraphrase the passage into simpler sentences.
But in this context, paraphrasing was difficult because there is over 3 sections to contrast.
I attach how I broke down this passage.
In the attachment, the green sentences are my process of thinking, and the blue ones are synonyms for paraphrasing.
If I made any mistake, or I fails to consider something, I'm all ears to you.

Thank you again !

GMATNinja and others, what is good timing on a passage this length (short) and difficulty?

Is managing ~1:40 per question with 75%+ accuracy sufficient for 720+ RC?

Thanks a lot

Hi Experts

In the last 2 sentences of 1st Para,

Researchers discovered that all asteroids obey strict limit on rotation rates except for 5 observed asteroids. All these 5 asteroids are less than 200 meters in diameter.

what does the phrase after comma 'with an abrupt cutoff for asteroids larger than that.' means?

GMATNinja
Could you please explain Q3?

It's really hard to extrapolate an RC score from this kind of information. For one thing, the difficulty level of the exact questions you miss will play into your score, and it's possible to have a relatively easy question on a tough passage. On the timing front, you're below the average time available for verbal section questions, which is great! But, of course, your overall time management depends on your CR and SC timing as well. If you take forever on CR/SC and don't see the last RC passage, then of course your RC score is going to be terrible even though your RC timing is fine.

The best way to assess your time management on the verbal section is to take an official practice test at mba.com, or a "fake test" using mba.com questions (see this video or this post for instructions to set this up).

I hope that helps a bit!

Here’s the relevant portion of the passage:

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 author first lays out that the rate at which asteroids rotate is limited for all but five asteroids, each of which is smaller than 200 meters in diameter. He/she goes on to detail that the exceptions cut off for asteroids larger than that. So in other words, all asteroids larger than 200 meters in diameter obey the strict limit on rate of rotation.

I hope that helps!

Question 3

The question asks about a prediction derived from the strength of the gravitational attraction of small asteroids. The passage talks about this gravitational attraction in the final sentence. It says:

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

So, small asteroids have weak gravity. As a result, impact fragments easily escape, and most small asteroids should be monolithic. With that in mind, let’s take a look at the answer choices.

Nowhere in the passage does the author suggest that small asteroids are few in number or that large asteroids are more common. Moreover, the relative scarcity of different sizes of asteroids is not connected to the gravitational pull of these asteroids. Eliminate (A).

As we identified above, the last sentence of the passage indicates that the weak gravitational pull of small asteroids will likely ensure that most small asteroids are monoliths. This is exactly what (B) says. Let’s keep (B).

In the second to last sentence of the passage, the author notes that “collisions among asteroids are relatively frequent.” He/she never suggests that small asteroids rarely collide with other asteroids. Eliminate (C).

(D) is tempting. The passage does seem to suggest that five small asteroids rotate faster than other asteroids. Perhaps, we could infer that small asteroids have faster rotation rates. But even that is a leap, and it is definitely not connected to the gravitational pull of small asteroids. Eliminate (D).

While the passage suggests that five small asteroids have very fast rotation rates, it does not indicate that only a few small asteroids have slow rotation rates. In fact, it’s possible that most other small asteroids have slow rotation rates. And the rotation rate of these asteroids is not connected to their gravitational pull. Eliminate (E).

(B) is the only answer choice remaining, and it is correct.

I hope that helps!

Hello! I am still a little confused on this answer. Since the five asteroids are exceptions to the rule, wouldn't they rather be a part of the rubble with speeds higher than the usual speed?
Since the answer suggests them to be monolith, and monolith asteroids can have any speed (Since the speed distribution for monoliths is a bell curve), they are no longer exceptions to the rule right?
GMATNinja

The “rule” found in the passage is that MOST of the observed asteroids obey a strict limit on their rate of rotation. So the rule isn't about rubble piles or monoliths. Instead, it’s a rule that observed asteroids, in general, tend to follow.

Then, the passage indicates that five asteroids are exceptions among observed asteroids, not among rubble piles. This means that the five asteroids are unique among other asteroids, not unique among rubble piles or monoliths. Then, the passage goes on to explain that the five asteroids can exceed the typical rate of rotation limit because they are monoliths.

I hope that helps!

Hi GMATNinja

While reading, I got confused a bit about clause below.

At first, I think the five observed asteroids DO obey a strict limit on RoR.
But after reading many comments, I just found that it should be

1. Is my understanding correct?
2. How can I prevent this mistake in the future? Should I focus on its meaning?

GMATNinja
VeritasKarishma
I understood why E is correct. Can you help to understand why B is incorrect?
The author of the passage mentions “escape velocity” (see line 22) in order to help explain which of the following?
(B) The speed with which impact fragments reassemble when they do not escape an asteroid’s gravitational attraction after a collision
Relevant line - 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
Acc to passage, the speed at which those bits move is compared with the escape velocity. Why can't we say that escape velocity is used to explain/"compare" the speed with which those fragments reassemble after a collision.

Sneha2021, good question! B is indeed very tempting (one of the hardest official traps, with 48% choosing it).

B has several correct elements, but we must make sure that every part of the answer choice is correct.

The author's point in mentioning "those bits will usually move slower than their mutual escape velocity" is that the bits cannot escape, and therefore the pieces reassemble, and therefore the large asteroids persist. As you noted, therefore E is correct: "The tendency for large asteroids to persist after collisions."

The problem with B is that it focuses on "the SPEED with which impact fragments reassemble". The author does not attempt to explain the SPEED of reassembling; rather, the author explains that the pieces DO reassemble, to support the author's larger conclusion, 1 sentence above: "The evident conclusion—that asteroids larger than 200 meters across are multicomponent structures or rubble piles — agrees with recent computer modeling of collisions...". Another similar conclusion is stated, 2 sentences below: "Because collisions among asteroids are relatively frequent, most large bodies have already suffered this fate."

Incorrect options will sometimes look relevant so we need to read the passage very carefully.

Question: Escape velocity is mentioned to explain what?

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.

What do we gather from this?
Large asteroids are usually rubble piles. When collision happens, they are blasted into bits but those bits are slower than their mutual escape velocity (so they do not fly far away from each other). Hence they reassemble back into one big mass of rubble (their mutual gravity pulls them together). Most collisions happens frequently, most big asteroids have collided and reformed into big piles of rubble.


Why did they mention escape velocity? To explain you why the small pieces don't fly away and why they reassemble.

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

Escape velocity does not explain at what speed the fragments reassemble. We know it takes them a few hours but why, we don't know. Escape velocity doesn't explain. Escape velocity explains why they reassemble and not fly away.

(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

Correct. It explains why large asteroids remain large (because even after collision, they reassemble because the speeds of their bits are slower than escape velocity).

Answer (E)

I got question 4 right when I was attempting the passage under timed environment. Now when I am re-evaluating, I can quickly eliminate options B, C, and D, but I am finding it harder to eliminate option A. GMATNinja and other experts, can someone please help with this?

Question 4

Take another look at the section in question:
The key thing here is that MOST pieces of the asteroid get reassembled back together. In other words, the author mentions "escape velocity" to explain how these large asteroids still exist -- gravity pulls them back together.

(A) says almost the opposite:

Sure, these asteroids must become a bit smaller when a few pieces manage to escape. However, the reason why the author brings up escape velocity is to explain why big asteroids stick together, NOT to focus on the small pieces that do escape. Most pieces DON'T escape, which explains why large asteroids persist.

(A) is out, and (E) is the correct answer to question 4.

I hope that helps!