Question

A man weighing 80 kg is standing in a trolley weighing 320 kg. The trolley is resting on friction-less 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

Initially momentum of the system is zero.
Due to motion of man, trolley along with the man will travel in backwards direction.
$\therefore 80\times 1+(80+320){\upsilon }^{\prime }=0$
or ${\upsilon }^{\prime }=-0.2m/s$
Man travels forward with the speed of 1 m/s and backwards with the speed of 0.2 m/s.
So, net velocity of the man is 0.8 m/s.
$\therefore d=\upsilon \times t=0.8\times 4=3.2$