Question

a ball of mass 0.5 kg slows down from a speed of 5m/s to 3m/s .calculate the change in kinetic energy and also the work done?

Answer 1

Change in kinetic energy

= 1/2 mv^2 – 1/2 mu^2

= 1/2 ( 0.5 ) ( v^2 – u^2 )

= 1/2 * 0.5 ( 25 - 9 )

= 0.25 * 16

= 4 J

Work done = Force × Displacement

or change in kinetic energy = 4J

Hope it helps!

Answer 2

According to work energy theorem, total work done = change in kinetic energy.
 = final kinetic energy - initial kinetic energy.

= $\frac{1}{2}mv^2 - \frac{1}{2}mu^2$
= $\frac{1}{2}m (v^2-u^2)$

= $\frac{1}{2}\times 0.5\times (3^2-5^2)$

= $0.25\times (9-25)$
= $0.25 \times(-16) = -4\:J$

Negative sign indicate that the work done is against motion and the kinetic energy has decreased.

Answers:
1 Change in kinetic energy = -4 J
2. Work done  = -4 J