A tennis ball is dropped on a horizontal smooth surface. It bounces back to its original position after hitting the surface. The force on the ball during the collision is proportional to the length of compression of the ball. Which one of the following sketches describes the variation of its kinetic energy $K$ with time $t$ most appropriately? The figures are only illustrative and not to the scale.

A particle $(\mathrm{m}=1\; \mathrm{kg})$ slides down a frictionless track $(AOC)$ starting from rest at a point $A$ (height $2\; \mathrm{m}$ ). After reaching $\mathrm{C}$, the particle continues to move freely in air as a projectile. When it reaching its highest point $P$ (height $1 \;\mathrm{m}$ ). the kinetic energy of the particle (in $\mathrm{J}$ ) is : (Figure drawn is schematic and not to scale; take $\left.g=10 \;\mathrm{ms}^{-2}\right)$

A ball moving with a velocity of $6\, m/s$ strikes an identical stationary ball. After collision each ball moves at an angle of $30^o$ with the original line of motion. What are the speeds of the balls after the collision ?

In a system of particles, internal forces can change (for the system)

A bomb of mass $9\, kg$ explodes into two pieces of masses $3\, kg$ and $6\, kg$. The velocity of mass $3\, kg$ is $16\, m/s$. The $KE$ of mass $6\, kg$ is ............ $\mathrm{J}$

A bomb of mass $10\, kg$ explodes into two pieces of masses $4\, kg$ and $6\, kg$. If  kinetic energy of $4\, kg$ piece is $200\, J$. Find out kinetic energy of $6\, kg$ piece