$A$ man of mass $80\, kg$ is standing in an elevator which is moving with an acceleration of $6\, m/s^2$ in the upward direction. The apparent weight of the man will be ......... $N$ $(g = 10\, m/s^2)$.

$A$ block of mass $m$ is kept in an elevator which starts moving downward with an acceleration $a$ as shown in the figure. The block is observed by two observers $A$ and $B$ for a time interval $t_0$. The observer $B$ is on the ground (inertial frame). What is the work done by the pseudo force on the block as observed by observer $B$?

$A$ spring balance is attached to the ceiling of a lift. $A$ man hangs his bag on the spring and the spring balance reads $49 \,N$, when the lift is stationary. If the lift moves downward with an acceleration of $5 \,m/s^2$, the reading of the spring balance will be $(g = 9.8 \,m/s^2)$. (in $\,N$)

$A$ boy of $50 \, kg$ is in a lift moving down with an acceleration of $9.8 \, m/s^2$. The apparent weight of the boy is ........... $N$ $(g = 9.8 \, m/s^2)$.

Two blocks of masses $m_1$ and $m_2$ are connected with a massless unstretched spring and placed over a plank moving with an acceleration '$a$' as shown in the figure. The coefficient of friction between the blocks and the platform is $\mu$.

$A$ point mass $m$ is suspended from a light thread of length $l$, fixed at $O$, and is whirled in a horizontal circle at a constant speed as shown. From your point of view, stationary with respect to the mass, the forces on the mass are