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Homework Help: Projectile motion of a cannon ball

  1. Sep 21, 2010 #1
    a ball is fired from a cannon at an angle of 40 degrees to the horizontal and it travels 300m before hitting the side of a cliff which is 10 meters higher than the cannons position.
    Determine the initial velocity.

    The ball has a negative velocity when it hits the cliff.

    My attempt:
    Where v = the balls initial velocity
    y component of velocity = -9.81t + Vsin40

    integrate this and get

    y position = .5*-9.8t^2 + vsin40t

    x component of velocity = vcos40

    integrate this and get

    x position = vcos40t

    Using the expression for x velocity, solve for t at 300m in the x direction and get the expression

    Sub this into the expression for the y position above and solve for v.

    I'm unsure if this is the correct way to go about doing this. The velocity I ended up with is 42.7124ms^-1 which seems a bit slow for the distance it covers.
  2. jcsd
  3. Sep 22, 2010 #2
    Your method is correct.
    I check your answer, but I got the initial speed is 48.8 m/s.
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