Question

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?

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.

Answer 2

Answer:

The net work done is 45.31J

Work done on a body is equal to an increase in energy of a body

The formula for work done is

W = force x distance

Given:

mass = 145g

Speed = 25m/s

We will need to find the distance using one of the equations of motion

$v^{2} = u^{2} + 2as\\\\Where u = 0\\\\25^{2} = 0^{2} + 2 * 10 * s\\625 = 20s\\divide through by 20\\\\\frac{625}{20} = \frac{20s}20} \\s = 31.25m$

Force = m x g

Convert the mass from g to kg by dividing by 1000

m = 145g

m = 145/1000

m = 0.145kg

Force = 0.145 x 10

Force = 1.45N

Work done = 1.45 * 31.25

Work done = 45.31J

Hence, the net work done is 45.31J

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