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 speed 1 m/s. Then after 4 s, his displacement relative to ground will be :

• A. 4.5 m
• B. 5 m
• C. 8 m
• D. 3.2 m

Answer 1

The correct option is D 3.2 m

In $1s$, man has walked, $4m/s\times 1s=4m$, with respect to the trolley.

As position of the CoM stays same, let the distance moved by trolley be $x$ in direction opposite to that of man.

So net diplacement of man is $(4-x)m$

Thus, $M_{man}\times (4-x)=M_{trolley}x$

$⟹80(4-x)=320x⟹x=320/400=0.8m$

So net displacement of man in $1s$ is, $4-0.8=3.2m$

Option D is correct.