A man of mass M is standing on a plank kept in a box. The plank and box as a whole has mass m. A light string passing over a fixed smooth pulley connects the man and box. If the box remains stationary, find the tension in the string and the force exerted by the man on the plank.
(m+M)g2, (M−m)g2
Let the tension in the string be T and force exerted by the man on plank be N.
For the (m+M) system, net external force is 2T−(m+M)g.
For equilibrium, 2T−(m+M)g=0⇒T=(m+M)g2
Now, for the man, Mg=T+N
Solving we get, N=(M−m)g2