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Homework Help: A 30 kg child moving at 4 m/s jumps onto a 50 kg sled that is initiall

  1. Oct 18, 2011 #1
    1. The problem statement, all variables and given/known data
    A 30 kg child moving at 4 m/s jumps onto a 50 kg sled that is initially on a frictionless surface. Find the speed of the child-sled system after it jumps onto the sled

    I know the solution looks like this
    but i don't know why and what that equation is?
  2. jcsd
  3. Oct 18, 2011 #2


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    Re: Energy

    You should look up momentum or collisions thru a web search or text. It is the conservation of momentum equation for a 'totally inelastic' collision. Please indicate why this collision is totally inelastic; but in general, momentum is always conserved in any type collision when no external forces are present.
  4. Oct 19, 2011 #3
    Re: Energy

    Thanks PhantomJay. I read about it and it makes sense. We haven't learned momentum yet so I was confused on what they were doing.
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