What is linear momentum ? Write its $SI$ unit.

Explain -product of mass and velocity is important in producing effect of force.

A spherical body of mass $100 \mathrm{~g}$ is dropped from a height of $10 \mathrm{~m}$ from the ground. After hitting the ground, the body rebounds to a height of $5 \mathrm{~m}$. The impulse of force imparted by the ground to the body is given by : (given $\mathrm{g}=9.8 \mathrm{~m} / \mathrm{s}^2$ )

The time in which a force of $2 \,N$ produces a change of momentum of $0.4\,kg – m{s^{ – 1}}$ in the body is ……… $\sec$

A particle of mass $m$ moving with velocity $u$ makes an elastic one dimensional collision with a stationary particle of mass $m$. They are in contact for a very short time $T$. Their force of interaction increases from zero to $F_0$ linearly in time $T/2$, and decreases linearly to zero in further time $T/2$. The magnitude of $F_0$ is