(a) State two quantities that are conserved in an elastic collision.

(b) A machine gun fires bullets of mass $0.014 \mathrm{kg}$at a speed of $640{ \mathrm{ms}}^{-1}$.

(i) Calculate the momentum of each bullet as it leaves the gun.

(b) A machine gun fires bullets of mass $0.014 \mathrm{kg}$at a speed of $640{ \mathrm{ms}}^{-1}$.

(ii) Explain why a soldier holding the machine gun experiences a force when the gun is firing.

(b) A machine gun fires bullets of mass $0.014 \mathrm{kg}$at a speed of $640{ \mathrm{ms}}^{-1}$.

(iii) The maximum steady horizontal force that a soldier can exert on the gun is $140 \mathrm{N}$. Calculate the maximum number of bullets that the gun can fire in one second.

Two railway trucks are travelling in the same direction and collide. The mass of truck $\mathrm{X}$ is $2.0\times {10}^4 \mathrm{kg}$ and the mass of truck $\mathrm{Y}$ is $3.0\times {10}^4 \mathrm{kg}$. This graph shows how the velocity of each truck varies with time.

 Copy and complete the table.

Two railway trucks are travelling in the same direction and collide. The mass of truck $\mathrm{X}$ is $2.0\times {10}^4 \mathrm{kg}$ and the mass of truck $\mathrm{Y}$ is $3.0\times {10}^4 \mathrm{kg}$. This graph shows how the velocity of each truck varies with time.

(b) State and explain whether the collision of the two trucks is an example of an elastic collision.

Two railway trucks are travelling in the same direction and collide. The mass of truck $\mathrm{X}$ is $2.0\times {10}^4 \mathrm{kg}$ and the mass of truck $\mathrm{Y}$ is $3.0\times {10}^4 \mathrm{kg}$. This graph shows how the velocity of each truck varies with time.

Determine the force that acts on each truck during the collision.