In the following problem,indicate the correct direction of the friction force acting on the cylinder,which is pulled on a rough surface by a constant force $F$. $A$ spool is pulled horizontally by a constant force $F$ applied below the center of mass. Which of the following diagrams correctly shows the direction of the friction force?

$A$ truck of mass $2800 \ kg$ is moving at a speed of $15 \ m/s$. $A$ frictional force of $500 \ N$ and a forward force of $1200 \ N$ act on it. The distance covered by the truck in $10 \ s$ is .......... $m$.

$A$ disc of mass $0.2 \ kg$ is kept floating in air without falling by vertically firing bullets each of mass $0.05 \ kg$ on the disc at the rate of $10$ bullets per second. If the bullets rebound with the same speed,then the speed of each bullet is (Acceleration due to gravity $g = 10 \ m \ s^{-2}$) (in $m \ s^{-1}$)

$A$ force of $mg$ is applied to block $B$ to keep the system in equilibrium. Find the value of $T_1$.

Give the magnitude and direction of the net force acting on:
$(a)$ a drop of rain falling down with a constant speed,
$(b)$ a cork of mass $10\; g$ floating on water,
$(c)$ a kite skillfully held stationary in the sky,
$(d)$ a car moving with a constant velocity of $30\; km/h$ on a rough road,
$(e)$ a high-speed electron in space far from all material objects,and free of electric and magnetic fields.

$A$ force $F = Kt$ (where $t$ is the time in seconds and $K = 2 \, N/s$) is applied on a $2 \, kg$ block at $t = 0$ as shown in the figure. The displacement of the $8 \, kg$ block until the time when the $2 \, kg$ block starts slipping on the $8 \, kg$ block will be (coefficient of friction between the $2 \, kg$ block and the $8 \, kg$ block is $0.2$ and between the $8 \, kg$ block and the surface is zero,$g = 10 \, m/s^2$).