$A$ particle of mass $m$ with an initial velocity $u\hat{i}$ collides perfectly elastically with a mass $3m$ at rest. It moves with a velocity $v\hat{j}$ after collision. Then, $v$ is given by:

$A$ body of mass $m$ moving with velocity $v$ undergoes a head-on elastic collision with another body of mass $2m$ which is initially at rest. The ratio of the kinetic energy $(K.E.)$ of the colliding body before and after the collision is: (in $: 1$)

When a moving body collides with a stationary body of $n$ times its mass,then the amount of kinetic energy transferred to the stationary body is

$A$ steel ball of radius $2 \,cm$ is at rest on a frictionless surface. Another steel ball of radius $4 \,cm$ moving with velocity of $81 \,cm \,s^{-1}$ collides elastically with the ball which is at rest. After collision, the ball with radius of $2 \,cm$ moves with a speed of:

$A$ body of mass $M$ moving at speed $V_{0}$ collides elastically with a mass $m$ at rest. After the collision,the two masses move at angles $\theta_{1}$ and $\theta_{2}$ with respect to the initial direction of motion of the body of mass $M$. The largest possible value of the ratio $M/m$,for which the angles $\theta_{1}$ and $\theta_{2}$ will be equal,is:

$A$ point mass $M$ moving with a certain velocity collides with a stationary point mass $M / 2$. The collision is elastic and in one-dimension. Let the ratio of the final velocities of $M$ and $M / 2$ be $x$. The value of $x$ is