A body falling from a height of $10\,m$ rebounds from hard floor. If it loses $20\%$ energy on the impact, then coefficient of restitution is

A steel ball of radius $2\, cm$ is at rest on a frictionless surface. Another ball of radius $4\,cm$ moving at a velocity of $81 \,cm/sec$ collides elastically with first ball. After collision the smaller ball moves with speed of ............. $\mathrm{cm} / \mathrm{sec}$

Explain oblique collision.

A bullet of mass $0.012\;kg$ and hortzontal speed $70\; m s ^{-1}$ strikes a block of wood of mass $0.4\; kg$ and instantly comes to rest with respect to the block. The block is suspended from the celling by means of thin wires. Calculate the height to which the block rises. Also, estimate the amount of heat produced in the block.

Consider elastic collision of a particle of mass $m $ moving with a velocity $u$ with another particle of the same mass at rest. After the collision the projectile and the struck particle move in directions making angles ${\theta _1}$and ${\theta _2}$respectively with the initial direction of motion. The sum of the angles. ${\theta _1} + {\theta _2},$ is......$^o$

In an elastic collision of two particles the following is conserved