Two persons $A$ & $B$ are throwing ball of $200\  g$ on wall as shown in figure. Balls strike wall perpendicularly at same point height $2\ m$ from ground. Ball strike wall elastically at same time and returns back to $A$ & $B$, at same time. They again repeat the same. What is the average force on wall ..................... $\mathrm{N}$ (take $g = 10\  m/s^2$)

 A lorry and a car moving with the same $K.E.$  are brought to rest by applying the same retarding force, then

A ball is dropped from height $5\,\,m$. The time after which ball stops rebounding if coefficient of restitution between ball and ground $e = 1/2$, is ............. $\mathrm{sec}$

A ball of $0.4\,kg$ mass and a speed of $3\, m/s$ has a head-on, completely elastic  collision with a $0.6-kg$ mass initially at rest. Find the speeds of both balls after the  collision:

The bob $A$ of a simple pendulum is released when the string makes an angle of ${45^o}$with the vertical. It hits another bob $B$ of the same material and same mass kept at rest on the table. If the collision is elastic

A sphere of mass $m $ moving with a constant velocity $u$ hits another stationary sphere of the same mass. If $e$  is the coefficient of restitution, then the ratio of the velocity of two spheres after collision will be