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Homework Help: Dropping the ball

  1. Mar 30, 2007 #1
    So, here is the problem:

    I have a .535kg ball that I drop from an unkown height, to create an impact with a force of 6.8 Joules.

    I need to figure out what height to drop the ball from.

    I figure it has something to do with accleration due to gravity and Netwons law F=mA or possibly a kinetic energy equation.

    Right now I am scrambling to find the answer.

    Can anyone please help?
  2. jcsd
  3. Mar 31, 2007 #2


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    Gold Member

    You need to define mathematically what 'impact' is. If you drop something it acquires momentum. A force is exerted when there's a change in the momentum, like when the dropped thing hits the ground. The force depends on how quickly the object stops. The faster it stops the greater the force.
  4. Mar 31, 2007 #3
    Well, if you define impact as energy, which is suggested by your units, then what you need to do is apply the Conservation of Energy. In your case, you wan't a KE of 6.8J, hence you can equtae it with potential energy.
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