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Homework Help: HELP A question on Kinematics in 2D & 3D?

  1. Sep 21, 2008 #1
    HELP!!! A question on Kinematics in 2D & 3D?

    1. The problem statement, all variables and given/known data

    A gun is placed at the base of a hill whose slope makes an angle alpha with the horizontal. If the gun is set at an angle theta with the horizontal and has a muzzle velocity Vo, find the distance, measured along the hill, at which the bullet will fall.


    3. The attempt at a solution
    I know that I need to separate this question in to two equations/ two 1D problems (x-axis and y axis)
    Velocity for x = Vo* cos(Θ-α) - g * t * sin(α)
    X = Xo + Vo * t * cos(Θ-α) - 0.5 * g * t^2 * sin(α)
    Velocity for y = Vo* sin(Θ-α) - g * t * cos(α)
    Y = Yo + Vo * t * sin(Θ-α) - 0.5 * g * t^2 * cos(α)

    But how can i figure out Vo, Θ, α, Xo, t and Yo

    Please help me.
     
  2. jcsd
  3. Sep 22, 2008 #2

    Kurdt

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    Re: HELP!!! A question on Kinematics in 2D & 3D?

    Seems you've set your axes up so that the x axis runs along the slope. What condition occurs at the point of impact that you can use. That is, what will the value of the y axis be?
     
  4. Sep 22, 2008 #3
    Re: HELP!!! A question on Kinematics in 2D & 3D?

    Do you mean set subsitute one of the variable in y equation from x equation?
     
  5. Sep 22, 2008 #4

    Kurdt

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    Re: HELP!!! A question on Kinematics in 2D & 3D?

    Yes. What will the y position be with the coordinates you chose when the ball lands? You can then get an expression for the flight time and sub it into the x equation which will give you the distance when t is the total flight time.
     
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