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Simple question with SUVAT equations. Watch

    • Thread Starter

    Hi there.

    I'm taking AS Physics this year and just having a bit of trouble with some parts of this homework we've been set, I'd be grateful if omeone could help.

    "An object in Free Fall has a constant acceleration of 9.81 ms-2. It goes past 2 light gates. The time interval between passing the first and the second is 0.269s. The distance between is 1.36m.
    1) What is the object's speed as it passes the first light gate?
    2) At what height from the first light gate was it dropped?"

    I was kind of completely lost with this, but I tried this:

    S = 1.36 m
    T = 0.269 s
    A = 9.81 ms-2
    U = speed at first light gate

    So s = ut + 1/2at^2;
    1.36 = u * 0.269 + 9.81 * 0.269^2

    Moving u over leves s/t:

    u = 1.36/0.269 + (9.81 * 0.269^2)/2
    u = 2.88 ms-1 (3sf)

    But the textbook gives the answer as 3.74 ms-1?
    I suspect it's something to do with my atrocious re-arranging skills...

    Forget this post

    EDIT: completely misread quaetion
    • Thread Starter

    (Original post by GHOSH-5)
    s = ut + 1/2at^2
    ut = s - 1/2at^2
    u = (s - 1/2at^2)/t

    now try.

    Thanks, I've been looking at this for like 20 minutes now and it finally just clicked!

    How did you move the s and ut round which made neg half from stage1 to stage 2?
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