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Projectile rock hitting a moving van problem

  1. Feb 22, 2006 #1
    I have equations for the following problem and an answer, but I am not sure if they are correct:

    Suzie (a geology student) is attacking a police van during a demonstration for peace and love at the University. The van is escaping at 3.2 m/s. Suzie throws her rock when the back of the van is 5.0 meters away. The rock leaves her hand at 1.6 meters above the ground, with a speed of 9.0 m/s and an angle of 37 degrees above the horizon. The rock hits and dents the back door of the van. Find the position of the van (relative to Suzie) when the rock hits it. Also find the height of the rock when it hits the van.

    Xf = Xi + Vo*t + .5 a*t^2
    Xf = 5 + 3.2 t + 0

    Vxf = Vxi = 7.19 m/s after breaking 9.0 m/s at 37 degrees down into x and y components

    Xf = Xi + Vxo * t
    Xf = 7.19*t

    Vyf = Vyo - gt
    Vyf = 5.42 - 9.8 t

    Yf = Yo + Vyo * t - 4.9 t^2
    Yf = 1.6 + 5.42 (1.25) - 4.9 (1.25)^2

    The answers I got:

    time = 1.25 seconds
    Xf relative to Suzie = 9.01 meters
    Vf = .7 m above the ground

    Is there a mistake?
  2. jcsd
  3. Feb 22, 2006 #2
    I haven't checked the numbers but the method looks ok.

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