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# The energy an animal must expend to move uphill is proportional to its

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Manager
Joined: 12 Mar 2013
Posts: 247
The energy an animal must expend to move uphill is proportional to its  [#permalink]

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24 Jan 2017, 20:55
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6
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Difficulty:

55% (hard)

Question Stats:

63% (01:36) correct 37% (01:49) wrong based on 199 sessions

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The energy an animal must expend to move uphill is proportional to its body weight, whereas the animal’s energy output available to perform this task is proportional to its surface area. This is the reason that small animals, like squirrels, can run up a tree trunk almost as fast as they can move on level ground, whereas large animals tend to slow down when they are moving uphill.

Which one of the following is an assumption on which the explanation above depends?

(A) The amount of energy needed to move uphill is no greater for large animals than it is for small animals.
(B) Small animals can move more rapidly than large animals can.
(C) The ratio of surface area to body weight is smaller in large animals than it is in small animals.
(D) There is little variation in the ratio of energy output to body weight among animals.
(E) The amount of energy needed to run at a given speed is proportional to the surface area of the running animal.

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Director
Affiliations: CrackVerbal
Joined: 03 Oct 2013
Posts: 533
Location: India
GMAT 1: 780 Q51 V46
Re: The energy an animal must expend to move uphill is proportional to its  [#permalink]

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24 Jan 2017, 23:16
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let us simplify what the question says -

Energy required = constant * body weight
Energy output = constant * surface area.

Now, (energy output) / (energy required) = constant * (surface area) / (body weight)

We are told that smaller mammals can run almost as fast as they can on ground, whereas large mammals tend to slow down.

this means that energy output is more than able to meet the energy required in smaller mammals (that is why they do not slow down).
Whereas it is less in larger mammals (they slow down because they are not able to meet energy requirements)

Hence, ratio > 1 (in larger mammals) and < 1 (in smaller mammals). If we compare the two ratios, we get -

(surface area)/ (body weight) [for small mammals] > (surface area)/ (body weight) [for large mammals]

Which option states this? Option C.

A - Incorrect.
Not true. We know that they require more energy as their body weight is more.

B - Incorrect.
We do not know whether they can actually run at higher speeds than larger mammals. All we know is that they do not slow when moving uphill but larger mammals do.
We do not have any idea about their actual speeds.
Moreover, we have data only when they move uphill. Other scenarios are not known.

D - Incorrect.
We know that (energy output/surface area) is constant. We don't have any idea about (energy output/ body weight).

E - Incorrect.
Energy required is proportional to the body weight. We cannot infer about surface area.
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Manager
Joined: 07 Apr 2018
Posts: 72
Location: United States
Concentration: General Management, Marketing
GPA: 3.8
Re: The energy an animal must expend to move uphill is proportional to its  [#permalink]

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24 Nov 2018, 11:57
conclusion: large animals tend to slow down when they are moving uphill(compared to flat ground).

Energy required = constant * body weight
Energy output = constant * surface area.
Now, (energy output) / (energy required) = constant * (surface area) / (body weight)= constant_3
it does not say why the big animal will run slow uphill.

So if a cheetah and a squirrel run on the ground , the squirrel will win as per the OA.
Re: The energy an animal must expend to move uphill is proportional to its &nbs [#permalink] 24 Nov 2018, 11:57
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