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Math Help - Area under velocity-time graph

  1. #1
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    Area under velocity-time graph

    Hi

    I was asked to estimate the area under a graph plotted from some data.
    Please could you have a look at the attached document – it contains the data and the graph and the equations used.
    My graph and wrong answer are shown, as is the mark scheme’s correct answer.
    I don’t understand why my answer was wrong.
    Can someone explain why?

    Thanks for your time.

    Fred
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  2. #2
    MHF Contributor ebaines's Avatar
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    Re: Area under velocity-time graph

    This is why I've never liked estimation problems - there is not a single correct answer. Both your answer and their answer are good estimates, so both are correct. Your method works out to be better than theirs, at least in terms of accuracy. I suppose that the person who came up with this problem felt that using the point (400,40) as the corner of the trapezoid just looks better than point (360,40), maybe because the value at t=400 is close to 40 m/s (closer than what your line indicates), so maybe he felt that would give a better estimate. If not for the way the graph flattens out toward the end their answer would be better than yours.
    Last edited by ebaines; November 20th 2013 at 01:03 PM.
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  3. #3
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    Re: Area under velocity-time graph

    Thanks, ebaines.
    That may well be how the examiner was thinking.
    Pity my answer was marked as wrong!
    Thank you.
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