$A$ man weighing $60 \text{ kg}$ is in a lift moving down with an acceleration of $1.8 \text{ ms}^{-2}$. The force exerted by the floor on him is:

$A$ 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

$A$ boy whose mass is $50\,kg$ stands on a spring balance inside a lift. The lift starts to ascend with an acceleration of $2\,m/s^2$. The reading of the machine or balance $(g = 10\,m/s^2)$ is ........ $kg$.

$A$ simple pendulum is attached to a block which slides without friction down an inclined plane $ABC$ having an angle of inclination $\alpha$ as shown below. While the block is sliding down,the pendulum oscillates in such a way that at its mean position,the direction of the string is

$A$ container of mass $m$ is pulled by a constant force $F$. Inside the container,a second block of the same mass $m$ is placed,connected to the wall by a massless spring of constant $k$. Initially,the spring is at its natural length. Find the velocity of the container at the instant the compression in the spring is maximum for the first time.

$A$ 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 ......... $N$ $(g = 10\, m/s^2)$.