What is the work done on an object moving with a constant speed?

$A$ bullet when fired at a target with a velocity of $100\,m/s$ penetrates $1\,m$ into it. If the bullet is fired at a similar target with a thickness of $0.5\,m$,then it will emerge from it with a velocity of:

Two monkeys with the same mass stand on a branch at height $h$ above the horizontal jungle floor. Monkey $A$ steps off the branch holding the end of an inextensible rope of length $L$ whose other end is tied to another branch at height $H$,lets go at the bottom of the swing,and falls freely to the floor,as shown below. Monkey $B$ steps off and falls straight downward. Then,neglecting air resistance but not the tension in the rope,the total work $W$ done on each monkey and the speed $v$ with which each hits the floor are as follows:

State and establish the principle of conservation of mechanical energy.

$A$ block of mass $100 \, g$ moves on a rough surface. The heat produced when its velocity changes from $10 \, m/s$ to $5 \, m/s$ is ....... $J$.

The rain drop of mass $1 \text{ g}$, starts with zero velocity from a height of $1 \text{ km}$. It hits the ground with a speed of $5 \text{ m/s}$. The work done by the unknown resistive force is . . . . . . $J$. (take $g = 10 \text{ m/s}^2$)