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. 5 metres
B. 4.8 metres
C. 3.2 metres
D. 3.0 metres

Answer

C

Explanation

Displacement of the man on the trollye `=1xx4=4m` Now applying conservation of linear momentum `80xx1+400v or v=-(1)/(5)` m/sec.
The distance travelled by the trollye `=-0.2xx4=-0.8 m`
(In opposite direction to the man.)
Thus, the relavtive displacement of the man with the ground `=(4-0.8)=3.2 m`