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Simple Energy Problem Im missing something

  1. Oct 18, 2006 #1
    The coyote, whose mass is 20.0kg, is chasing the roadrunner when the coyote accidentally runs off the edge of a cliff and plummets to the ground 30.0m below. What force does the ground exert on the coyote as he makes a coyote-shaped dent .420m deep in the ground?

    I know that he hits the ground with a force of 6,000J becasue the PE=mgh at the top, Assuming that none of his enery is lost to air resistance he will hit the ground with that same force because all of the potential energy will be converted into kinetic energy. Im just not sure how to get the force. I know F=ma but that seems just to simple.

    Any help at all will be appreciated.

    Thanks for looking,

  2. jcsd
  3. Oct 18, 2006 #2


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    Do you mean, what is the force which the ground exerts on the coyote while he's been slammed into the ground? If so, use the fact that the change of kinetic energy from the position above the ground to the position when the coyote is stuck in the ground (where his speed = 0) equals the sum of work of gravity (i.e. the coyote's weight) and the work of the force which the ground exerts on him, along the displacement of 0.42 [m]. I hope I didn't miss something.
  4. Oct 18, 2006 #3

    Im not sure i understand what your are saying. Are you saying that the force is just mg? Or am i not reading correctly
  5. Oct 19, 2006 #4


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    No, the force is not just mg. While being slammed into the ground, the forces acting on the coyote are gravity, and the force which the ground exerts on the coyote (in the opposite direction than gravity), which is the force you need to find.
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