$A$ $4 \ kg$ disk slides over level ice toward the east at a velocity of $1 \ m/s$,as shown. The disk strikes a post and rebounds toward the north at the same speed. The change in the magnitude of the eastward component of the momentum of the disk is ............. $kg \cdot m/s$.

$A$ small mass $m$ is launched from the top of a cliff with speed $V$ at an angle of $30^{\circ}$ above the horizontal. When the mass reaches the ground,its velocity is directed at $45^{\circ}$ below the horizontal. Which one of the following choices is the magnitude of the total impulse that was imparted to the mass during its flight? Ignore air resistance.

$A$ student attempts to pull himself up by tugging on his hair. He will not succeed because:

$A$ machine gun fires $20$ bullets per second into a target. Each bullet weighs $150 \, g$ and has a speed of $800 \, m/s$. Find the force necessary to hold the gun in position.

The average force necessary to stop a hammer having momentum $50 \ N-s$ in $0.25 \ s$ is ...... $N$.

$A$ $140\,g$ ball,in horizontal flight with a speed of $39.0\,m/s$,is struck by a bat. After leaving the bat,the ball travels in the opposite direction with a speed of $39.0\,m/s$. If the impact time $\Delta t$ for the ball-bat collision is $1.20\,ms$,calculate the average force in $N$ acting on the ball.