A $15 \mathrm{g}$ bullet is fired from a gun of mass $3 \mathrm{kg}$. If the speed of bullet just after firing is $300 \mathrm{m} {\mathrm{s}}^{-1}$, what is the recoil speed of gun?

An empty rail car of mass $100 \mathrm{kg}$ is at rest on the railway track. A boy of mass $40 \mathrm{kg}$ running with a speed of $5 \mathrm{m} {\mathrm{s}}^{-1}$ jumps on the rail car. The speed of the (car boy) system is how much?

The initial situation of two moving objects is shown in the figure. Suppose, after collision the two objects stick. What will be velocity of the two object system?

A bullet of mass $20 \mathrm{g}$ is fired horizontally with a velocity of  $100 \mathrm{m} {\mathrm{s}}^{-1}$from a pistol of $1.5 \mathrm{kg}$. Calculate the recoil velocity of the pistol.

A boy of mass $50 \mathrm{kg}$ running at $5 \mathrm{m} {\mathrm{s}}^{-1}$ jumps on to a trolley of $20 \mathrm{kg}$ travelling in the same direction at $1.5 \mathrm{m} {\mathrm{s}}^{-1}$. Find their common velocity.