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Math Help - very simply projectile question

  1. #1
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    Question very simply projectile question

    1. A particle is projected with an initial velocity of V m/s and attains a maximum height of 12.5m before landing 100m from the point of projection. Calculate the value of V.

    Can someone check my answer for this?
    2. The displacement, x, of a particle moving in a straight line is represented by the equation: x = 5cos4t
    Find a) The initial velocity of the particle
    b) initial acceleration of the particle


    a)  x = 5cos4t

     v = x' = -20sin4t

    initial velocity.. when t = 0, v = 0

    b)  a = x" = -80cos4t

    when t =0, a = -80


    Thanks in advance
    Last edited by differentiate; September 26th 2009 at 02:24 AM.
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  2. #2
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    Quote Originally Posted by differentiate View Post
    1. A particle is projected with an initial velocity of V m/s and attains a maximum height of 12.5m before landing 100m from the point of projection. Calculate the value of V.

    use these three equations, all derived from the basic equations for kinematics w/ constant acceleration.

    v_{oy} = \sqrt{2gh}

    t = \frac{2v_{oy}}{g}

    v_x = \frac{\Delta x}{t}

    then ...

    v_o = \sqrt{(v_{oy})^2 + (v_x)^2}

    Can someone check my answer for this?
    2. The displacement, x, of a particle moving in a straight line is represented by the equation: x = 5cos4t
    Find a) The initial velocity of the particle
    b) initial acceleration of the particle


    a)  x = 5cos4t

     v = x' = -20sin4t

    initial velocity.. when t = 0, v = 0

    b)  a = x" = -80cos4t

    when t =0, a = -80

    both correct
    ...
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  3. #3
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    Thanks skeeter. umm... for g, can i say that it's 9.8 m/s? coz someone told me that you have to assume that it's 9.8
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  4. #4
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    Quote Originally Posted by differentiate View Post
    Thanks skeeter. umm... for g, can i say that it's 9.8 m/s? coz someone told me that you have to assume that it's 9.8
    If a numerical answer is required, yes. The question should make that clear.
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