Q21 - The energy an animal

[willaminic]

Hi

I have been thinking about this question for a long time and did not figure out why C is right, why is ratio even matters??? Thank you in advance.

[jardinsouslapluie5]

I don't understand the wrong answers explanation.

Just saying "nothing to do with uphill" does not show how it has nothing to do with.
I need more detailed explanation for wrong answers please.

[ttunden]

I don't understand the wrong answers explanation.

Just saying "nothing to do with uphill" does not show how it has nothing to do with.
I need more detailed explanation for wrong answers please.

I really don't understand this question. Can someone explain this further please?

[christine.defenbaugh]

Great questions, guys - let's rip this one apart from top to bottom:

PREMISE:
1) body weight = proportional to energy you need to move uphill
2) surface area = proportional to energy you have to move uphill
CONCLUSION: THAT'S why small animals don't slow down when going uphill, but large animals do slow down when going uphill

Hmm. Wait, why do large animals slow down? Well, if they didn't have as much energy for the job as they really needed, they'd slow down. And if an animal DID have plenty of energy for the job, they'd presumably move just as fast as they always do!

So, the conclusion is telling us that little critters have plenty of energy for their uphill task, while large animals don't have as much energy as they need for their uphill task. What does that mean? It might be tempting to blame it on just one piece of the puzzle, but both surface area and body weight matter here: one tells us how big the job is, and the other tells us the energy we have to do that job. We need to know how those two things relate.

Imagine if you have two dogs, Bob and Joe, and they each have the exact same surface area (so they have the same energy available to them). But Bob weighs twice as much as Joe! Because Bob's weight is higher, he needs more energy to move uphill than Joe does - but they have the same energy available. That would mean that Bob is going to move uphill slower than Joe - he needs more energy, but doesn't actually HAVE more energy.

Now imagine if you have two dogs of the exact same weight, Spot and Jack - so they need the same energy to move uphill. But Spot has twice as much surface area! So, Spot has a lot more energy available to him to use, for the same job. That means Spot is going to move faster uphill than Jack!

So, increasing the body weight will slow you down, but increasing the surface area will speed you up!

Now, back to the conclusion - the argument is using all this information about energy to conclude that this is the explanation for why large animals slow down. In order to make that connection, we need to know something about the relationship between body weight and surface area in the large animals vs the small animals.

If the two types of animals had the exact same ratio of surface area to body weight, then they have the same relationship between the energy they have and the energy they need, and we'd expect them to move at the same speed. If we were to increase the surface area alone, the animal would have more energy available, move faster, and that ratio would get larger. However, if we were to increase the body weight alone, that animal would need more energy, move slower, and that ratio would get smaller.

So, if we're going to blame all this energy relationship stuff for making large animals slow down, we must be assuming that this ratio of surface area to body weight is smaller in large animals! And that's exactly what (C) gives us!

Whew!

Let's take a quick look at the incorrect answers:

(A) If the amount of energy no greater for large animals, that would suggest that they don't weigh more than small animals, which seems unlikely. We certainly don't NEED them to weigh the same for this argument to work! In fact, the argument is more likely to work if they weigh MORE!
(B) We don't need them to be able to move more rapidly all the time, just uphill. And the argument tells us that they *can* move uphill faster, we're just trying to explain why.
(D) This seems related, but is actually talking about actual "output", while the information in the stimulus is all about either 1) energy available or 2) energy required. "Output" is the energy that actually gets used, and that's different!
(E) This introduces a new relationship between surface area and "energy required to run at a given speed", which seems to be talking about running on even ground - our argument was about the energy needed to move uphill! And this doesn't tell me anything about the difference between small and large animals!

I hope this helps clear a few things up on this difficult question!

[william.j.kwon]

So here is my question in relation to identifying/dissecting the premise-conclusion of this stimulus.

To me it seems that the author is providing his/her own explanation of weight and surface area in explaining the observation of squirrels and larger animals. (https://www.manhattanprep.com/lsat/foru ... t2020.html)
In that sense it seems much more logical to regard the entire observation of squirrels and large animals as the premise part and to consider the author's explanation as conclusion. I think it is much more natural to see the whole argument originating from one observation and reaching a particular conclusion that the author deems logical/plausible explanation.

Therefore I believe that it is better to put the stimulus as


Premise : Small animals run up a tree trunk fast while large animals slow down upon running uphill.
-->
Conclusion : Weight proportional to energy output and surface area to energy output

I would be more than glad if you could clarify on this.
Thanks in advance and excuse me for English not being my first language.

[hanhansummer]

I think adding specific number to this question is a good way to make some sense.

P:
body weight - energy must expend to move uphill
surface area - energy available to move uphill

C:
small animals run up fast, while large animals run slow.

We know that large animals probably have both larger body weight and surface area than small ones. So let's suppose large animals need to spend 100 energy to do the task and small animals 50. But to have large animals run slow and small animals run fast means the small ones must at least have as much available energy as they need (50) in order to run fast, while the large ones may do not have as much available energy as they need(let's say 80), so they run slow. So the key or necessary assumption is the ratio of s.f. to b.w. (energy available to energy requirement), or you can understand as a kind of evaluation that whether the animals have enough available energy to satisfy its energy consumption.

It's my understanding to this question.

[JinZ551]

B is fake comparison.

The stimulus is comparing the speed between an animal's climbing uphill and that of the same animal moving on level ground, not comparing between small and large animal speed.