A 145-g baseball is thrown so that it acquires a speed of 25 m/s. What was the net work done on the ball to make it reach this speed, if it started from rest?

Question

Cesar Sanford

Physics

24 May, 22:32

A 145-g baseball is thrown so that it acquires a speed of 25 m/s. What was the net work done on the ball to make it reach this speed, if it started from rest?

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Thomas Archer · Answer 1

When the ball has left your hand and is flying on its own, its kinetic energy is

KE = (1/2) (mass) (speed²)

KE = (1/2) (0.145 kg) (25 m/s) ²

KE = (0.0725 kg) (625 m²/s²)

KE = 45.3 Joules

If the baseball doesn't have rocket engines on it, or a hamster inside running on a treadmill that turns a propeller on the outside, then there's only one other place where that kinetic energy could come from: It MUST have come from the hand that threw the ball. The hand would have needed to do 45.3 J of work on the ball before releasing it.