$A$ particle of mass $m$,moving with a velocity $v$,makes an elastic collision in one dimension with a stationary particle of mass $m$. During the collision,they remain in contact with each other for an extremely small time $T$. Their force of contact with time is shown in the figure. Then $F_0 =$

$A$ body of mass $4\ kg$ collides head-on elastically with another body of mass $2\ kg$ kept at rest in free space. The time of collision is $0.02\ s$ and the average impulsive force acting on each body is $100\ N$. Find the velocity of the $2\ kg$ body after the impact. (in $m/s$)

Two identical spheres move in opposite directions with speeds $v_1$ and $v_2$ and pass behind an opaque screen,where they may either cross without touching (Event $1$) or make an elastic head-on collision (Event $2$).

$A$ ball of mass $m$ moving with velocity $V$ makes a head-on elastic collision with a ball of the same mass moving with velocity $2V$ towards it. Taking the direction of $V$ as positive,the velocities of the two balls after the collision are:

$A$ particle of mass $m_1$ collides with a particle of mass $m_2$ at rest. After the elastic collision,the two particles move at an angle of $90^{\circ}$ with respect to each other. The ratio $\frac{m_2}{m_1}$ is

$A$ ball of mass $2m$ and a system of two balls with equal masses $m$ connected by a massless spring are placed on a smooth horizontal surface (see figure). Initially, the ball of mass $2m$ moves with velocity $u_0$ along the line passing through the centres of all the balls and the spring, whereas the system of two balls is at rest. Assuming that the collision between the individual balls is perfectly elastic, the ratio of vibrational energy stored in the system of two connected balls to the initial kinetic energy of the ball of mass $2m$ is