$A$ $1000\, kg$ elevator rises from rest in the basement to the fourth floor,a distance of $20\, m$. As it passes the fourth floor,its speed is $4\, m/s$. There is a constant frictional force of $500\, N$. The work done by the lifting mechanism is

$A$ body of mass $5\,kg$ is moving with a momentum of $10\,kg\,m/s$. Now a force of $2\,N$ acts on the body in the direction of its motion for $5\,s$. The increase in the kinetic energy of the body is $...........J$.

$A$ body $A$ moving with momentum $P$ collides one-dimensionally with another stationary body $B$ of same mass. During impact,$A$ gives impulse $J$ to $B$. Then which of the following is/are correct?
$(a)$ The total momentum of $A$ and $B$ is $P$ before and after impact and $(P-J)$ during the impact.
$(b)$ During the impact,$B$ gives impulse of magnitude $J$ to $A$.
$(c)$ The coefficient of restitution is $\left[\frac{2 J}{P}-1\right]$.
$(d)$ The coefficient of restitution is $\left[\frac{2 J}{P}+1\right]$.

Explain why total linear momentum is conserved in an elastic collision,and define inelastic collision and perfectly inelastic collision.

$A$ stationary object of mass $10 \ kg$ is subjected to two mutually perpendicular forces of $4 \ N$ and $3 \ N$. What will be its kinetic energy after $10 \ s$?

In an elastic collision between disks $A$ and $B$ of equal mass but unequal radii,$A$ moves along the $x$-axis and $B$ is stationary before impact. Which of the following is possible after impact?