How do the rockets operate in space? Explain.

Two identical bullets are fired one by a light rifle and another by a heavy rifle with the same force. Which rifle will hurt the shoulder more and why?

Suppose a ball of mass $\mathrm{m}$ is thrown vertically upward with an initial speed $\mathrm{v}$, its speed decreases continuously till it becomes zero. Thereafter, the ball begins to fall downward and attains the speed $\mathrm{v}$ again before striking the ground. It implies that the magnitude of initial and final momentum of the ball is same. Yet, it is not an example of conservation of momentum. Explain why?