# A-level Physics (Advancing Physics)/Rockets, Hoses and Machine Guns/Worked Solutions

**1. A machine gun fires 300 5g bullets per. minute at 800ms ^{−1}. What force is exerted on the gun?**

**2. 1 litre of water is pumped out of a tank in 5 seconds through a hose. If a 2N force is exerted on the tank, at what speed does the water leave the hose?**

The flow rate is about 0.2 kg s^{−1}.

**3. If the hose were connected to the mains, what problems would there be with the above formula?**

The force would not be exerted on the tank, but would instead be referred back through the pipe - it is not gaining velocity at the nozzle.

**4. The thrust of the first stage of a Saturn V rocket is 34 MN, using 131000 kg of solid fuel in 168 seconds. At what velocity does the fuel leave the tank?**

**5. Escape velocity from the Earth is 11 km ^{−1}. What is the velocity of the rocket after the first stage is used up, if the total mass of the rocket is 3 x 10^{6} kg? How does this compare to escape velocity?**

This is 0.002% of escape velocity, hence the need for the other stages of the rocket.