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

## 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?

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]

Related Introductory Physics Homework Help News on Phys.org
haruspex
Homework Helper
Gold Member
Have another think about the first 0.5 on the right of the =.

0.5*(0.4Kg)*(20 m/s)^2 = 0.5 [(0.4Kg)(9.81 m/s^2)((4m) + 0.5(0.4Kg) Vf^2]
You're line of thinking is correct. Just stress on which energy needs to be reduced by half.

I tried reduce the Kinetic energy by half, but the answer is incorrect. Thanks.

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.

haruspex