$A$ bullet of mass $m$ moving with velocity $v$ strikes a suspended wooden block of mass $M$. If the block rises to a height $h$,the initial velocity of the bullet will be

Two bodies $A$ and $B$ of masses $20 \ kg$ and $5 \ kg$ respectively are at rest. Due to the action of a force of $40 \ N$ separately,if the two bodies acquire equal kinetic energies in times $t_A$ and $t_B$ respectively,then $t_A: t_B=$

Two identical particles are moving with same velocity $v$ as shown in the figure. If the collision is completely inelastic,then:

$A$ man throws a ball to a height of $12 \ m$,where it reaches with a speed of $12 \ m/s$. If the man throws the ball such that it just reaches this height,what percentage of energy would he have saved?

Is the statement "The work done by object $B$ on object $A$ is equal and opposite to the work done by object $A$ on object $B$" correct?

$A$ bolt of mass $0.3 \; kg$ falls from the ceiling of an elevator moving down with a uniform speed of $7 \; m s^{-1}$. It hits the floor of the elevator (length of the elevator $= 3 \; m$) and does not rebound. What is the heat produced by the impact? Would your answer be different if the elevator were stationary?