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What speed will the ball hit the ground?

  1. Apr 17, 2012 #1
    A ball has a mass of 240g. (which would be 0.24kg?) is moving through the air at 20.0m/s with a gravitational potential energy of 70J. With what speed will the ball hit the ground.

    Equations:

    Ek=mv^2/2 (kinetic energy)
    Eg=mgh (Gravitational potential energy)
    Ek=mgxdisplacement (if you don't have velocity?)

    I would appreciate ANY help...I don't get what I'm supposed to do.

    P.S. the answer in the book says it should be 31.4m/s :)
     
  2. jcsd
  3. Apr 17, 2012 #2
    You assume that the groud is zero potential: Then the initian kinetic energy is [itex]T_i =1/2mv_i^2[/itex]
    And the initial potential energy is 70J the 70J is all being converted to kinetic energy when it falls so make your equation and solve it:
    [itex] E_{initial}= 70J+T_i = E_{final}[/itex]
     
  4. Apr 18, 2012 #3
    Thank you :)
     
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