A body of mass m dropped from a height h reaches the ground with a speed of 0 . 8 g h . The value of work done by the air-friction is:

Step-by-step solution

K 1 + U 1 = K 2 + U 2 + W f W f : work done against friction 0 + m g h = 1 2 m v 2 + 0 + W f m g h = 1 2 m 0 . 64 g h + W f W f = 0.68 m g h Work done by friction W f ' = - W f = - 0.68 m g h