What physical quantity is represented by the area under the force-time graph?

"Momentum is the product of velocity and its magnitude." Is this statement true or false?

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

$A$ 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 $kg \cdot m/s$)

An athlete runs for some distance before taking a long jump. Why?

$A$ body of mass $m$ collides against a wall with a velocity $v$ and rebounds with the same speed. Its change of momentum is