Question

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

• A. 5 m
• B. 4.8 m
• C. 3.2 m
• D. 3.0 m

Answer 1

The correct option is C. 3.2 m

If the man starts walking on the trolley in the forward direction then whole system will move in backward direction with same momentum.

Momentum of man in forward direction = Momentum of system (man + trolley) in backward direction
$\Rightarrow 80\times 1=(80+320)\times v\Rightarrow v=0.2m/s$
So the velocity of man w.r.t. ground 1.0 - 0.2 = 0.8 m/s
$\therefore$Displacement of man w.r.t. ground = 0.8 $\times$ 4 = 3.2 m.