posted by nathan .
A 20g plastic ball is moving to the left at 30 m/s. How much work must be done th cause the ball to move to the right at 30 m/s?
Work must be done to stop the ball, which would be equal to the kinetic energy of the ball, or
The same work is needed to give the ball the same kinetic energy as before, but in the opposit direction, so
The total work required is W1+W2.