$A$ body of mass $2\,kg$ makes an elastic collision with a second body of mass $m$ at rest and continues to move in the original direction but with one-fourth of its original speed. What is the mass of the second body? ................ $kg$

Two identical balls $A$ and $B$ having velocities of $0.5 \, m s^{-1}$ and $-0.3 \, m s^{-1}$ respectively collide elastically in one dimension. The velocities of $B$ and $A$ after the collision respectively will be

$A$ particle of mass $m$ moving with kinetic energy $E$ collides head-on elastically with another particle of mass $2m$ at rest. After the collision,the kinetic energy of the first particle is:

$A$ sphere of mass $0.1\,kg$ is attached to a cord of $1\,m$ length. Starting from the height of its point of suspension,this sphere hits a block of the same mass at rest on a frictionless table. If the impact is elastic,then the kinetic energy of the block after the collision is ............. $J$.

$A$ ball hits the floor and rebounds. For this elastic collision case,which of the following is true?

Two balls $X(2 \ kg)$ and $Y(4 \ kg)$ approach each other with equal speeds of $10 \ ms^{-1}$. If the collision is perfectly elastic,then the new velocities of balls $X$ and $Y$ are respectively