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

Assertion $(A)$: In an elastic collision of two billiard balls,the total kinetic energy $(KE)$ is conserved during the short time of collision of the balls (i.e.,when they are in contact).
Reason $(R)$: Energy spent against friction does not follow the law of conservation of energy.

$A$ body of mass $2 \; kg$ initially at rest moves under the action of an applied horizontal force of $7 \; N$ on a table with coefficient of kinetic friction $= 0.1$. Compute the
$(a)$ work done by the applied force in $10 \; s$,
$(b)$ work done by friction in $10 \; s$,
$(c)$ work done by the net force on the body in $10 \; s$,
$(d)$ change in kinetic energy of the body in $10 \; s$,
and interpret your results.

$A$ motor drives a body along a straight line with a constant force. The power $P$ developed by the motor must vary with time $t$ according to

$A$ section of a fixed smooth circular track of radius $R$ in a vertical plane is shown in the figure. $A$ block is released from position $A$ and leaves the track at $B$. The radius of curvature of its trajectory when it just leaves the track at $B$ is:

$A$ body of mass $4 \,kg$ is moving with momentum of $8 \,kg \,m/s$. $A$ force of $0.2 \,N$ acts on it in the direction of motion of the body for $10 \,s$. The increase in kinetic energy in joules is