A ball falling freely from a height of $4.9\,m,$ hits a horizontal surface. If $e = \frac {3}{4}$ , then the ball will hit the surface, second time after .............. $\mathrm{s}$

Two equal masses ${m_1}$ and ${m_2}$ moving along the same straight line with velocities $+ 3 \,m/s$ and $-5\, m/s$ respectively collide elastically. Their velocities after the collision will be respectively

An unknown nucleus collides with a ${}^4He$ nucleus, and after the collision the two nuclei travel in perpendicular directions relative to each other. If kinetic energy is lost in the collision, the unknown nucleus must be 

Particle $A$ makes a perfectly elastic collision with another particle $B$ at rest. They fly apart in opposite direction with equal speeds. If their masses are $m_A$ and $m_B$ respectively, then

A stream of glass beads, each with a mass of $15\  gram$, comes out of a horizontal tube at a rate of $100\  per second$. The beads fall a distance of $5\  m$ to a balance pan and bounce back to their original height. How much mass(in $kg$) must be placed in the other pan of the balance to keep the pointer at zero?

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