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What's the speed of ball when travelling over the fence?

  1. Jan 25, 2015 #1
    1. The problem statement, all variables and given/known data
    Two girls are playing baseball in a park. The batter hits the 400-g ball with a speed of 20.0 m/s. It travels over the park's fence that is 4.00 m high. Assuming that the ball loses half of its energy to air resistance, at what speed does the ball travel over the fence?
    2. Relevant equations
    Ek = 0.5*m*v^2
    Ep = m*p*h


    3. The attempt at a solution
    0.5*(0.4Kg)*(20 m/s)^2 = 0.5 [(0.4Kg)(9.81 m/s^2)((4m) + 0.5(0.4Kg) Vf^2]
    My answer was wrong.
     
  2. jcsd
  3. Jan 25, 2015 #2

    haruspex

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    Have another think about the first 0.5 on the right of the =.
     
  4. Jan 25, 2015 #3
    You're line of thinking is correct. Just stress on which energy needs to be reduced by half.
     
  5. Jan 25, 2015 #4
    I tried reduce the Kinetic energy by half, but the answer is incorrect. Thanks.
     
  6. Jan 25, 2015 #5
    That's not what you've done in your equation. Check again.
     
  7. Jan 25, 2015 #6

    haruspex

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    Which term in your equation represents the initial KE? Where is that multiplied by one half?
     
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