A body of mass $m$ moving with velocity  $v$ elastic collides head on with another body of mass $2\,\,m$ which is initially at rest. The ratio of  $K.E.$  of the colliding body before and after collision will be

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 neutron makes a head-on elastic collision with a stationary deuteron. The fractional energy loss of the neutron in the collision is

In an elastic collision between disks $A$ and $B$ of equal mass but unequal radii, $A$ moves along the $x$ -axis and $B$ is stationary before impact. Which of the following is possible after impact?

The bob $A$ of a pendulum released from $30^o$ to the vertical hits another bob $B$ of the same mass at rest on a table as shown in Figure. How high does the bob A rise after the collision ? Neglect the size of the bobs and assume the collision to be elastic

A body of mass ${m_1}$ moving with a velocity$ 3 ms^{-1}$ collides with another body at rest of mass ${m_2}.$After collision the velocities of the two bodies are $2 ms^{-1} \,and \, 5ms^{-1}$ respectively along the direction of motion of ${m_1}$ The ratio $ \frac{m_1}{m_2}= $