A man weighing 80 kg is standing in a trolley weighing 320 kg. The trolley is resting on frictionless horizontal rails. If the man starts walking on the trolley with a speed of 1 m / s, then after 4 sec his displacement relative to the ground will be

If the man starts walking on the trolley in the forward direction then whole system will move in backward direction with same momentum. TROLLEY WILL MOVE BACK  WITH A VELOCITY V'=m vM +mIN 4 SEC the net distance of the man moved = x = v t - v't= 1×4-80×1320+80=3.2 m