Force Questions

A machine gun fires a bullet of mass $40\text{g}$ with a velocity $1200\text{m/s}$. The man holding it can exert a maximum force of $144\text{N}$ on the gun. How many bullets can he fire per second at the most?

A charged ball $B$ hangs from a silk thread $S$ which makes an angle $\theta$ with a large charged conducting sheet $P$, as shown in the figure. The surface charge density $\sigma$ of the sheet is proportional to:

Three charges $-q_1$, $+q_2$ and $-q_3$ are placed as shown in the figure. ($-q_1$ at origin, $+q_2$ at $(b,0)$, $-q_3$ at $(a\cos \theta ,a\sin \theta )$). The $x$ -component of the force on $-q_1$ is proportional to: