Given that a force $\vec{F}$ acts on a body for time $t_1$ and displaces the body by $\vec{d}$. In which of the following cases must the velocity of the body increase?

$A$ particle of mass $100 \ g$ is projected vertically upwards with a speed of $5 \ m/s$. What is the work done by the force of gravity during the time the particle returns to the starting point? (in $J$)

$A$ heavy box of $40\, kg$ is pushed along $20\, m$ by two coolies over a railway platform whose coefficient of friction with the box is $0.4$. The work done by the two coolies is: .................. $J$ (Take $g = 10\, m/s^2$)

$A$ block of mass $2 \,kg$ is pulled at a constant speed with a taut rope along a frictionless plane that is inclined at $30^{\circ}$. Then the work done by the tension in the rope in pulling it a distance $4 \,m$ along the inclined plane in joule is (acceleration due to gravity $= 10 \,ms^{-2}$)

$A$ force $\vec{F} = (5 \hat{\imath} - 2 \hat{\jmath} + 3 \hat{k}) \text{ N}$ acts on a body of mass $2 \text{ kg}$ and displaces it from position $\vec{r_1} = (3 \hat{\imath} + 2 \hat{\jmath} - \hat{k}) \text{ m}$ to $\vec{r_2} = (6 \hat{\imath} - \hat{\jmath} + 4 \hat{k}) \text{ m}$. The work done is: (in $\text{ J}$)

At time $t=0$,a particle starts moving along the $x$-axis. If its kinetic energy increases uniformly with time $t$,the net force acting on it must be proportional to