When a horse pulls a wagon,the force that causes the horse to move forward is the force

$A$ gun applies a force $F$ on a bullet which is given by $F = (100 - 0.5 \times 10^{5} t) \ N$. The bullet emerges out with a speed of $400 \ m/s$. Find the impulse exerted until the force on the bullet becomes zero (in $N \cdot s$).

$A$ wall is hit elastically and normally by $n$ balls per second. All the balls have the same mass $m$ and are moving with the same velocity $u$. The force exerted by the balls on the wall is

$A$ ping-pong ball of mass $m$ is floating in air by a jet of water emerging out of a nozzle. If the water strikes the ping-pong ball with a speed $v$ and just after collision the water falls dead,the rate of flow (in $kg/s$) of water in the nozzle is equal to

In projectile motion,two particles of masses $m_1$ and $m_2$ have velocities $\vec{V}_1$ and $\vec{V}_2$ respectively at time $t=0$. Their velocities become $\vec{V}_1^{\prime}$ and $\vec{V}_2^{\prime}$ at time $2t$ while still moving in air. The value of $[(m_1 \vec{V}_1^{\prime} + m_2 \vec{V}_2^{\prime}) - (m_1 \vec{V}_1 + m_2 \vec{V}_2)]$ is ($g =$ acceleration due to gravity).

$A$ particle moves in the $x-y$ plane under the influence of a force $\vec{F}$ such that its linear momentum is $\vec{P}(t) = \hat{i} \cos(kt) - \hat{j} \sin(kt)$. If $k$ is a constant,the angle between $\vec{F}$ and $\vec{P}$ will be: