The unit of impulse is

$A$ $2 \ kg$ object is initially at rest. It is acted upon by a force as indicated in the figure. Find the total work done by the force in $3 \ s$. (in $J$)

$A$ ball of mass $m$ moves with speed $v$ and strikes a wall normally and is reflected back normally. If its time of contact with the wall is $t$,find the force exerted by the ball on the wall.

$A$ golf ball of mass $50 \text{ g}$ placed on a tee is struck by a golf club. The speed of the golf ball as it leaves the tee is $100 \text{ m/s}$, and the time of contact with the ball is $0.02 \text{ s}$. If the force decreases to zero linearly with time, then the force at the beginning of the contact is (in $\text{ N}$)

$A$ machine gun fires a bullet of mass $65 \, g$ with a velocity of $1300 \, m/s$. The man holding it can exert a maximum force of $169 \, N$ on the gun. The number of bullets he can fire per second will be ............

$N$ number of balls,each of mass $m \ kg$,moving along the positive direction of the $x$-axis,strike a wall per second and return elastically. The velocity of each ball is $u \ m/s$. The force exerted on the wall by the balls in newtons is: