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Tiger beetles are such fast runners that they can capture

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Re: Tiger beetles are such fast runners that they can capture [#permalink] New post 09 Jan 2013, 14:18
wannahh wrote:
"they can capture virtually any nonflying insect."

C. The beetles maintain a fixed time interval between pauses, although when an insect that had been stationary
begins to flee
, the beetle increases its speed after its next pause.

is'nt C against the premise above?


well, the fact that the beetle increased its speed to capture a running insect doesn't mean it cannot capture it. It could well be the case that beetles can capture the insect (we don't whether it is flying or nonflying insect) after the chase.

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Re: Tiger beetles are such fast runners that they can capture [#permalink] New post 12 Jan 2013, 11:48
Marcab wrote:
Tiger beetles are such fast runners that they can capture virtually any nonflying insect. However, when running
toward an insect, the beetles intermittently stop, and then, a moment later, resume their attack. Perhaps they
cannot maintain their pace and must pause for a moment's rest; but an alternative hypothesis is that while
running tiger beetles are unable to process the resulting rapidly changing visual information, and so quickly go
blind and stop. Which of the following, if discovered in experiments using artificially moved prey
insects, would support one of the two hypotheses and undermine the other?
A. When a prey insect is moved directly toward a beetle that has been chasing it, the beetle immediately turns and
runs away without its usual intermittent stopping.
B. In pursuing a moving insect, the beetles usually respond immediately to changes in the insect's direction, and
pause equally frequently whether the chase is up or down an incline.
C. The beetles maintain a fixed time interval between pauses, although when an insect that had been stationary
begins to flee, the beetle increases its speed after its next pause.
D. If, when a beetle pauses, it has not gained on the insect it is pursuing, the beetle generally ends its pursuit.
E. When an obstacle is suddenly introduced just in front of running beetles, the beetles sometimes stop
immediately, but they never respond by running around the barrier.

OA
[Reveal] Spoiler:
soon

Though the same stimulus is available with different answer choices, I found this one to be a tough one. Explanations will be appreciated.



I'd go with option C and here's why.

The beetles maintain a fixed time interval between pauses: which means that they stop periodically to process visual information.

The beetle increase its speed after its next pause: The beetle doesn't stop due to tiredness; If it is tired, it cannot increase its pace after each break and still manage to maintain fixed(same) time intervals.

Cheers,

Jay
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Re: Tiger beetles are such fast runners that they can capture [#permalink] New post 18 Feb 2013, 21:58
I see that there are two versions of this question going around with a slight variation in answer choices that affects the correct answer. I will focus on the two contentious answer choices only in each of the two versions of this question.

Version# 1 (GMAT Prep)

B. In pursuing a moving insect, the beetles usually respond immediately to changes in the insect's direction, and pause equally frequently whether the chase is up or down an incline. - INCORRECT

A sudden change in insect direction is a big visual change. If the beetle were to require pauses/rest to adapt to rapidly changing visual information (Hypothesis# 2), then this hypothesis is undermined by the "immediate response" to change in insect direction, as mentioned in the first part of answer choice.
The inclined path is mentioned deliberately in the second part of this answer choice to help evaluate the first hypothesis that the beetle needs rest or break due to tiredness. Going up an incline always needs more muscular effort (read 'tiredness') to support component of body weight (remember 'mg sin theta' acting against the direction of motion), which implies more tiredness and resultant need for more frequent stops compared to going down an incline ('mg sin theta' acting in the direction of motion). Since this answer choice mentions that the beetle pauses equally frequently when going up or down the incline, even the first hypothesis is undermined.


C. The beetles maintain a fixed time interval between pauses, although when an insect that had been stationary begins to flee, the beetle increases its speed after its next pause. - CORRECT

Imagine a stationary insect really far away (lets exaggerate to 1 KM) that a beetle has somehow spotted and started to begin its attack by moving towards it. For the first 800 m, the insect has no idea that the beetle is reaching for it. For these 800 metres, the beetle is able to move linearly towards its target insect in intervals of 100m before it exhausts itself COMPLETELY and HAS TO take a rest. The timing of the rest is crucial to understanding this answer choice. One can argue that according to hypothesis 1 ('tiredness'), the beetle is able to rest long enough (exaggerate to 1 hour) after every 100m of run to fully recover its breath and energy, and start afresh for the next 100m. But this is not the case here, because otherwise during the last 200m of its attack (when the insect somehow discovers that it is being preyed and starts to flee), the beetle would not be able to run remaining 2x 100 m with any higher speed than what it had in all the first 8x 100m (remember we said the beetle exhausts itself completely in each of those 100m). The only plausible explanation is that tiredness is not a factor, and the beetle was stopping after every 100m for visual correction (can be safely assumed to take a 'fixed time'). This answer choice thus undermines one hypothesis (tiredness) over the other (visual correction).

I will respond to the other version of this question from OG later.
Re: Tiger beetles are such fast runners that they can capture   [#permalink] 18 Feb 2013, 21:58
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