$A$ machine gun fires a bullet of mass $40$ g with a speed of $600$ m/s. The person holding the gun can bear a maximum force of $168$ $N$ on it. The number of bullets that can be fired from the gun per second is

$A$ ball of mass $0.15 \, kg$ is dropped from a height $10 \, m$,strikes the ground,and rebounds to the same height. The magnitude of the impulse imparted to the ball is $(g = 10 \, m/s^2)$ nearly: (in $kg \cdot m/s$)

When a bullet is fired from a rifle, its momentum becomes $20 \,kg \cdot m/s$. If the velocity of the bullet is $1000 \,m/s$, then what is its mass?

Two identical billiard balls strike a rigid wall with the same speed but at different angles,and get reflected without any change in speed,as shown in the figure. What is
$(i)$ the direction of the force on the wall due to each ball?
$(ii)$ the ratio of the magnitudes of impulses imparted to the balls by the wall?

$A$ $40 \ g$ ball dropped from a certain height bounces back from the horizontal ground without losing mechanical energy. If its speed is $10 \ m/s$ just before making contact with the ground,and the average value of the force of the ground on the ball is $16 \ N$ while the ball and ground are in contact,how long were they in contact in milliseconds $(ms)$?

Consider the following statement: When jumping from some height,you should bend your knees as you come to rest,instead of keeping your legs stiff. Which of the following relations can be useful in explaining the statement?