When two identical masses,one of which is at rest,undergo an oblique elastic collision,what is the angle between the two bodies after the collision (in $^{\circ}$)?

$A$ ball of mass $0.1 \ kg$ undergoes a head-on collision with a stationary ball of unknown mass. If the $0.1 \ kg$ ball rebounds with $1/3$ of its original speed,the mass of the second ball is .......... $kg$.

$A$ heavy body moving with a velocity of $6\,ms^{-1}$ collides elastically with a light body (whose mass is half of the mass of the heavy body) at rest. The velocity of the light body will be (in $ms^{-1}$):

$A$ particle of mass $m$ moving with velocity $v$ makes a perfectly elastic collision with a simple pendulum bob of mass $m$. After the collision,the maximum height attained by the bob is:

$A$ moving body with mass $m_1$ strikes a stationary mass $m_2$. What should be the ratio $\frac{m_1}{m_2}$ so as to decrease the velocity of the first body by $1.5$ times after the collision?

$A$ ball of mass $m$ moving with speed $u$ undergoes a head-on elastic collision with a stationary ball of mass $nm$. What is the fraction of the kinetic energy transferred to the heavier ball?