$A$ body of mass $1\,kg$ collides head-on elastically with a stationary body of mass $3\,kg$. After the collision,the smaller body reverses its direction of motion and moves with a speed of $2\,m/s$. The initial speed of the smaller body before the collision is $..........\,m/s$.

$A$ body of mass $30 \ kg$ moving with a velocity $20 \ ms^{-1}$ undergoes a one-dimensional elastic collision with another ball of the same mass moving in the opposite direction with a velocity of $30 \ ms^{-1}$. After the collision,the velocities of the first and second bodies respectively are:

$A$ body of mass $m$ moving with velocity $v$ collides with a stationary body of mass $2m$. The fraction of kinetic energy lost by the body of mass $m$ is:

$A$ block of mass $m$ slides with speed $v$ on a frictionless table towards another stationary block of mass $m$. $A$ massless spring with spring constant $k$ is attached to the second block as shown in the figure. The maximum distance the spring gets compressed is

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

When two bodies collide elastically,then