A body of mass $1000 \mathrm{~kg}$ is moving horizontally with a velocity $6 \mathrm{~m} / \mathrm{s}$. If $200 \mathrm{~kg}$ extra mass is added, the final velocity (in $\mathrm{m} / \mathrm{s}$ ) is:

A machine gun of mass $10\,kg$ fires $20\,g$ bullets at the rate of $180$ bullets per minute with a speed of $100\,m s ^{-1}$ each. The recoil velocity of the gun is $………….\,m/s$

An open water tight railway wagon of mass $5 \times 10^3 kg$ coasts at an initial velocity $1.2 m/s$ without friction on a railway track. Rain drops fall vertically downwards into the wagon. The velocity of the wagon after it has collected $10^3 kg$ of water will be ………….. $\mathrm{m}/ \mathrm{s}$

A bullet of mass $5 \,g$ is shot from a gun of mass $5 \,kg$. The muzzle velocity of the bullet is $500\, m/s$. The recoil velocity of the gun is ……….. $m/s$

A shell of mass $m$ moving with velocity $ v$ suddenly breaks into $2$ pieces. The part having mass $m/4$ remains stationary. The velocity of the other shell will be