$A$ wall is hit elastically and normally by $n$ balls per second. All the balls have the same mass $m$ and are moving with the same velocity $u$. The force exerted by the balls on the wall is

Two bodies $A$ and $B$ collide as shown in Fig. $(i)$ and $(ii)$. Which statement is true?

$A$ particle is acted upon by a force whose components' variations with time are shown in the diagrams. The magnitude of the change in momentum of the particle in $0.1\,s$ is:

Why can it be said that there is no such thing as an isolated force in nature?

$A$ particle moves in the $xy$-plane under the action of a force $\vec{F}$ such that the components of its linear momentum $\vec{p}$ at any time $t$ are $p_x = 2\cos t$ and $p_y = 2\sin t$. The angle between $\vec{F}$ and $\vec{p}$ at time $t$ is ........... $^o$.

Two particles of masses $m_1$ and $m_2$ in projectile motion have velocities $\vec{v}_1$ and $\vec{v}_2$ respectively at time $t = 0$. They collide at time $t_0$. Their velocities become $\vec{v}_1'$ and $\vec{v}_2'$ at time $2t_0$ while still moving in air. The value of $|(m_1\vec{v}_1' + m_2\vec{v}_2') - (m_1\vec{v}_1 + m_2\vec{v}_2)|$ is