Two persons $A$ and $B$ are throwing a ball of mass $200 \ g$ at a wall as shown in the figure. The balls strike the wall perpendicularly at the same point at a height of $2 \ m$ from the ground. The balls strike the wall elastically at the same time and return back to $A$ and $B$ at the same time. They repeat this process. What is the average force exerted on the wall (in $N$)? (Take $g = 10 \ m/s^2$)

$A$ body of mass $100 \ gm$ moves with a constant speed along a circular path of radius $r$. What is the work done during one complete revolution?

$A$ $0.5 \, kg$ block moving at a speed of $12 \, ms^{-1}$ compresses a spring through a distance of $30 \, cm$ when its speed is halved. The spring constant of the spring in $N m^{-1}$ is:

Write the similarity between various forms of energy.

Which physical quantity is conserved in both elastic and inelastic collisions?

$A$ bullet of mass $10 \ g$ pierces through a plate $A$ of mass $500 \ g$ and then gets embedded into a second plate $B$ of mass $1.49 \ kg$ as shown in the figure. Initially,the two plates $A$ and $B$ are at rest and move with the same velocity after the collision. The percentage loss in the initial kinetic energy of the bullet when it is between the plates $A$ and $B$ is . . . . . . (Neglect any loss of material of the plates during the collision).