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Homework Help: Solving for Speed for Projectile Motion

  1. Nov 3, 2007 #1
    A person standing at the edge of a seaside cliff kicks a stone over the edge with a horizontal speed of 18 m/s. The cliff is 52 m above the water's surface. (Use GUESS method).

    C) With what speed does it strike the water? Answer: V=36.67

    I have already solved for time it takes to reach the water which is 3.26 s. The distance between the base of the cliff and where the stone lands is 58.64 m.

    I cannot figure out what the velocity is because I assume it would only be the vertical motion. The equation for the vertical motion is y =1/2(a)(t)^2 but there's nothing about velocity. I've already tried putting this equation into the one for horizontal but it ends up with a totally different number.

    Please show me how to solve this.
  2. jcsd
  3. Nov 3, 2007 #2


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    When the stone hits the water, it has both an x and y component of velocity. Use the motion equations in each direction that relate velocity with time in each direction, to get these components, then think pythagorus.
  4. Nov 3, 2007 #3
    Thank you soooo much. I figured it out.
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