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    Name:  ImageUploadedByStudent Room1368551868.437611.jpg
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Size:  181.1 KB can someone tell me why the time doesn't cancel as I couldn't get it to work and it only works when the t is squared?


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    (Original post by zachariou1)
    Name:  ImageUploadedByStudent Room1368551868.437611.jpg
Views: 66
Size:  181.1 KB can someone tell me why the time doesn't cancel as I couldn't get it to work and it only works when the t is squared?


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    To put it simple you cnt do tht bcuz s and -ut are seperate at the top so u cnt just divide the top by t only if the top was sut could u do tht dyu understand?
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    You only need to find the acceleration: therefore -
    S=2500km = 2500000m
    u= 0
    a = ?
    t = 30m = 1800s

    and so then rearrange S=ut+1/2*at ² to give a=s/(1/2*t ²) - note that the 'ut' can be got rid of as U=0
    and so the just put in the numbers to give: 2500000/(1/2*1800²) = 1.543209876ms-2 which is roughly equal to 2
    Hope this helped!
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    (Original post by Revisionbug)
    To put it simple you cnt do tht bcuz s and -ut are seperate at the top so u cnt just divide the top by t only if the top was sut could u do tht dyu understand?
    You have divided one half of the fraction by t but not the other half, you must do both sides otherwise it doesn't stay equal!
    Think of the fraction (11 - 4) / 4
    You can split that into 11/4 - 4/4 or 2.75 - 1 = 1.75
    If however, you cancel the 4 from just the RH numerator you would get:
    11 - 4/4 = 10 which is incorrect.

    [s - ut] / t² can be rewritten as s/t² - ut/t²
    However, you have split it into s - u/t which is something different so it won't work.
    You must divide every term of the fraction when you're cancelling something out.
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    Thanks guys, stupid me didn't realise u was 0 should really have listed out what each term is. Thanks a lot!


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