$A$ steel sphere of radius $1.2 \ cm$ collides with a second steel sphere at rest. If the collision is elastic and after the collision the first sphere continues to move in its initial direction with a velocity of $\frac{7}{9}$ times its initial velocity,then the radius of the second sphere is (in $cm$)

An object of mass $M$ is much heavier than another object of mass $m$. The heavy object moving with speed $v$ undergoes an elastic collision with the light object at rest. What will be the speed of the light object after the collision?

$A$ proton of mass $m$ collides elastically with a particle of unknown mass $M$ at rest. After the collision, the proton and the unknown particle are seen moving at an angle of $90^\circ$ with respect to each other. The mass of the unknown particle is:

$A$ particle of mass $m$ moving with a velocity $\vec{V}$ makes a head-on elastic collision with another particle of the same mass initially at rest. The velocity of the first particle after the collision will be:

What happens when two identical bodies moving in opposite directions undergo a perfectly elastic collision?

$A$ ball of mass $m$ moving with speed $v$ collides elastically with an identical stationary ball which is initially at rest. After collision,the first ball moves at an angle $\theta$ to its initial direction and has speed $(v/3)$. The second ball moves in a straight line after the collision. Then,the speed of the second ball after the collision is: