Question

An 8 kg ball is moving at 4 m/s. Work is done on the ball to give it a speedof 12 m/s. What is the ball's initial kinetic energy? What is the ball's finalkinetic energy? What work was done on the ball?

Answer 1

Given,

The mass of the ball, m=8 kg

The initial velocity of the ball, u=12 m/s

The final velocity of the ball v=12 m/s

The initial kinetic energy of the ball is given by,

`K_1=(1)/(2)mu^2`

On substituting the known values,

`\begin{gathered} K_1=(1)/(2)*8*4^2 \\ =64\text{ J} \end{gathered}`

Thus the initial kinetic energy is 64 J

The final kinetic energy is given by,

`K_2=(1)/(2)mv^2`

On substituting the known values,

`\begin{gathered} K_2=(1)/(2)*8*12^2 \\ =576\text{ J} \end{gathered}`

Thus the final kinetic energy is 576 J

The work done on the ball is given by the change in the kinetic energy of the ball.

Therefore the work done on the ball is

`\begin{gathered} W=K_2-K_1 \\ =576-64 \\ =512\text{ J} \end{gathered}`

Therefore the work done on the ball is 512 J