(i) The cause of increases in kinetic energy when a man starts running without his feet slipping on ground is asked to two students. Their answers are– Harshit: Cause of increase in kinetic energy is work done by friction force. Without friction the man cannot run. Akanksha: Cause of increase in kinetic energy is work done by internal (muscle) forces of the body. Who is right? (ii) An inextensible rope is hanging from a tree. A monkey, having mass m, climbs to a height h grabbing the rope tightly. The monkey starts from rest and ends up hanging motionlessly on the rope at height h. (a) How much work is done by gravity on the monkey? (b) How much work is done by the rope on the monkey? (c) Using work – energy theorem, explain the increase in mechanical energy of the monkey.

Answer

(i) Akanksha is right. (ii) a -mgh
(b) 0
(c) Internal (muscle) forces of the body perfom work