A man weighing `80 kg` is standing on a trolley weighting `320 kg`. The trolley is resting on frictionless horizontal rails. If the man starts walking on the trolley along the rails at speed `1 m//s` (w.r.t. to trolley) then after `4 s` his displacement relative to the ground will be :

Options

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

Answer

C

Explanation

If the amn starts walking on the trolley in the forward direction, then whole system will move in backward direction with the same momentum.
Momentum of mas in forward direction=Momentum of system (man+trollry) in backward direction implies `80xx1=(80+320)xxv` implies `v=0.2m//s`
So the velocity of man w.r.t. ground `1.0-0.2=0.8m//s`
:. Displacement of man w.r.t. ground `=0.8xx4`
`=3.2m` .