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Homework Help: Finding u using SUVAT

  1. May 4, 2004 #1
    I am currently doing a project involving an object sliding down a slope and falling freely for a given height afterwards. The horizontal distance is recorded, as is the angle of the slope. I have been trying to create an equation for u (the initial speed) from this data, but I haven't been able to. We are given that:

    y = x(tan[theta]) - ((4.9x^2)/(u^2))(1+tan^2[theta])

    y = vertical displacement (known)
    x = horizontal displacement (recorded)
    [theta] = slope angle (recorded)
    u = initial speed (required)

    This seems to be a slight variation on a few other problems I've seen on this forum, and try as I have, I haven't been able to relate that help to my situation - mainly because I have to use SUVAT.

    I can't seem to arrange the equation in a suitable form to easily give 'u'. I'd be really grateful for any help you could give me.


    Last edited: May 4, 2004
  2. jcsd
  3. May 4, 2004 #2


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    y = x(tan[theta]) - ((4.9x^2)/(u^2))(1+tan^2[theta])

    Can't you write:


    What's SUVAT by the way?
  4. May 4, 2004 #3
    y = x(tan[theta]) - ((4.9x^2)/(u^2))(1+tan^2[theta])

    ((4.9x^2)/(u^2))(1+tan^2[theta]) = x(tan[theta]) - y

    (4.9x^2)(1+tan^2[theta]) = (x(tan[theta]) - y)(u^2)

    (u^2) = (4.9x^2)(1+tan^2[theta]) / (x(tan[theta]) - y)
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