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

  • Thread starter Hoyin
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  • #1
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Homework Statement


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?

Homework Equations


Ek = 0.5*m*v^2
Ep = m*p*h


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.
 

Answers and Replies

  • #2
haruspex
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Have another think about the first 0.5 on the right of the =.
 
  • #3
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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.

You're line of thinking is correct. Just stress on which energy needs to be reduced by half.
 
  • #4
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I tried reduce the Kinetic energy by half, but the answer is incorrect. Thanks.
 
  • #5
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I tried reduce the Kinetic energy by half, but the answer is incorrect. Thanks.
That's not what you've done in your equation. Check again.
 
  • #6
haruspex
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I tried reduce the Kinetic energy by half, but the answer is incorrect. Thanks.
Which term in your equation represents the initial KE? Where is that multiplied by one half?
 

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