$A$ particle of mass $m$ is at rest at the origin at time $t = 0$. It is subjected to a force $F(t) = F_0e^{-bt}$ in the $x$-direction. Its speed $v(t)$ is depicted by which of the following curves?

When a force $F$ given by $F=(6 \hat{i}-18 \hat{j}+10 \hat{k}) \text{ N}$ acts on a body,it imparts an acceleration of $8 \text{ m/s}^2$. Find the mass of the body.

$A$ constant retarding force of $50\; N$ is applied to a body of mass $20\; kg$ moving initially with a speed of $15\; m/s$. How long (in $sec$) does the body take to stop?

$A$ 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 $\text{ kg}$)

An object with mass $5 \ kg$ is acted upon by a force,$\vec{F}=(-3 \hat{i}+4 \hat{j}) \ N$. If its initial velocity at $t=0$ is $\vec{v}=(6 \hat{i}-12 \hat{j}) \ ms^{-1}$,the time at which it will just have a velocity along the $y$-axis 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 ........... $N$.