What is dynamics?

The time taken by a force of $2 \ N$ to produce a change of momentum of $0.4 \ kg \ m \ s^{-1}$ in a body is: (in $s$)

$A$ ball of mass $0.2 \, kg$ moves with a velocity of $20 \, m/s$ and it stops in $0.1 \, s$; then the force on the ball is ........... $N$.

$A$ $4 \ kg$ object has a velocity of $3.0 \hat{i} \ m/s$ at some instant. Eight seconds later,its velocity is $(8.0 \hat{i} + 10.0 \hat{j}) \ m/s$. Assuming that the object is subjected to a constant net force,the magnitude of the force is

An object of mass $3\,kg$ is at rest. If a force $\vec{F} = (6t^2\hat{i} + 4t\hat{j})\,N$ is applied on the object,then the velocity of the object at $t = 3\,s$ will be

$A$ particle of mass $m$ is moving in a straight line with momentum $p$. Starting at time $t = 0$,a force $F = kt$ acts in the same direction on the moving particle during time interval $T$ so that its momentum changes from $p$ to $3p$. Here $k$ is a constant. The value of $T$ is