An average force of $125\,N$ is applied on a machine gun firing bullets each of mass $10\,g$ at the speed of $250\,m/s$ to keep it in position. The number of bullets fired per second by the machine gun is:

An object with a mass $10 \, kg$ moves at a constant velocity of $10 \, m/s$. $A$ constant force then acts for $4 \, s$ on the object and gives it a speed of $2 \, m/s$ in the opposite direction. The impulse acting on the object is ......... $N \cdot s$.

$A$ ball of mass $150 \, g$ moving with a velocity of $12 \, m/s$ hits a bat and returns with a velocity of $20 \, m/s$ in the opposite direction within $0.01 \, s$. The force exerted by the bat on the ball is ........... $N$.

Figures $(a)$,$(b)$,$(c)$ and $(d)$ show the variation of force with time. The impulse is highest in which figure?

$A$ ball of mass $0.5\, kg$ moving with a velocity of $2\, m/s$ strikes a wall normally and bounces back with the same speed. If the time of contact between the ball and the wall is $1\, ms$,the average force exerted by the wall on the ball is ......... $N$.

Swimming is possible on account of