Question

A man weighing 80 kg is standing on a trolley weighing 320 kg. The trolley is resting on frictionless horizontal rails. If the man starts walking on the trolley along the rails at a speed of one metre per second, then after 4 seconds, his displacement relative to the ground will be :(a) 5 metres (b) 4.8 metres(c) 3.2 metres (d) 3.0 metres

Answer 1

Let trolley's velocity be v and it's mass be m and man's velocity be V and his mass be M, then we have

m*v = (M+m)*V

we have m = 320kg,M = 80kg, V = 1m/s

since man has moved 4 s, distance moved by trolley -0.2*4 = -0.8 m

man has moved 4m but trolley has moved 1m in opposite direction.

therefore, displacement of man with respect to ground=

4 - 0.8 = 3.2 m