Question

A ball of mass 0.5 kg slows down from a speed of 5 m/s to that of 3 m/s. Calculate the change in kinetic energy of the ball.

Answer 1

Change in kinetic energy $=\frac{1}{2}m{v}^2-\frac{1}{2}m{u}^2=\frac{1}{2}m(v^2-u^2)=\frac{1}{2}\times 0.5(3^2-5^2)=-4J$

The minus sign shows that there is a decrease in KE.