Consider a drop of rain water having mass 1 g falling from a height of 1 km. It hits the ground with a speed of 50 ms-1. Take 'g' constant with a value 10ms-2. The work done by the (i) gravitational force and the (ii) resistive force of air is

Here, m=1 g=10-3 kg,h=1 km=1000 m,v=50 m s-1,g=10 m s-2(i) The work done by the gravitational force =mgh=10-3×10×1000=10 J(ii) The total work done by gravitational force and the resistive force of air is equal to change in kinetic energy of rain drop.∴Wg+Wr=12mv2-010+Wr=12×10-3×50×50 or Wr=-8.75 J