What is dynamics?

$A$ 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 ........... $N$.

$A$ force $\vec{F}=(40 \hat{i}+10 \hat{j}) \, N$ acts on a body of mass $5 \, kg$. If the body starts from rest,its position vector $\vec{r}$ at time $t=10 \, s$ will be -

An object of mass $2 \, kg$ is placed at rest in a frame $S_1$ moving with velocity $10 \hat{i} + 5 \hat{j} \, m/s$ and having acceleration $5 \hat{i} + 10 \hat{j} \, m/s^2$. The object is also seen by an observer standing in a frame $S_2$ moving with velocity $5 \hat{i} + 10 \hat{j} \, m/s$. Calculate the net force acting on the object with respect to the $S_1$ frame.

$A$ body of mass $500\,g$ moves along the $x$-axis such that its velocity varies with displacement $x$ according to the relation $v = 10\sqrt{x}\,m/s$. The force acting on the body is $...........\,N$.

$A$ force $(2 \hat{i} + \hat{j} - \hat{k}) \text{ N}$ acts on a body, which is initially at rest. At the end of $20 \text{ s}$, the velocity of the body is $(4 \hat{i} + 2 \hat{j} - 2 \hat{k}) \text{ ms}^{-1}$. The mass of the body is: (in $\text{ kg}$)