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Collision and impulse

  1. Mar 27, 2008 #1
    [SOLVED] collision and impulse

    1. The problem statement, all variables and given/known data
    A 1.0 kg ball drops vertically onto a floor, hitting with a speed of 20 m/s. It rebounds with an initial speed of 5 m/s.
    (a) What impulse acts on the ball during the contact?
    kg·m/s

    (b) If the ball is in contact with the floor for 0.020 s, what is the average force exerted on the floor?
    N



    2. Relevant equations
    p=m*v
    deltap=J
    F=m(deltav)/deltat


    3. The attempt at a solution

    For (a) i used p=m*v and deltap=J

    so I got (1*-20)-(1*5)=-25

    and for (b) i used that F=(m*deltav)/deltat

    which came out to be... 1(-25)/.020=0.5 N

    both answers were wrong and I'm not sure what is wrong with the formulas I used...

    Any help is appreciated! Thanks!
     
  2. jcsd
  3. Mar 27, 2008 #2
    25/0.020=1250
     
  4. Mar 27, 2008 #3
    For a) the impulse is P_after - P_before and not P_before - P_after.

    For b) see The reply of Mikelepore. I think you need to add the force of gravity as well.
     
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