Question

A ball of mass 0.5 kg slows down from a speed of 10 m s^-1 to that of 6 m s^-1. Calculate the change in the kinetic energy of the ball.

Answer 1

Mass of ball = 0.5 kg

Initial velocity = 10m s^-1

Final velocity = 6 m s^-1

∴ Initial K.E. = ${\displaystyle \frac{1}{2}m{v}^2}$

= ${\displaystyle \frac{1}{2}\times 0.5\times 10\times 10}$

= 25 J

Final K.E. = ${\displaystyle \frac{1}{2}m{v}^2}$

= ${\displaystyle \frac{1}{2}\times 0.5\times 6\times 6}$

= 9 J

Change in K.E. = 25 – 9 = 16 J

∴ K.E. decreases by 4 J