$A$ body is moving with a uniform velocity of $2 \, m/s$ on a rough level surface. The frictional force on it is $10 \, N$. If the body moves with a velocity of $4 \, m/s$,the force of friction will be ........ $N$.

$A$ man of mass $60 \, kg$ slides down a pole by applying a force of $600 \, N$ on it. If the coefficient of friction between the hands and the pole is $0.5$,then the acceleration of the man is ............ $m/s^2$ $(g = 10 \, m/s^2)$.

$A$ block of mass $50\, kg$ slides over a horizontal distance of $1\, m$. If the coefficient of friction between their surfaces is $0.2$,then the work done against friction is ......... $J$.

$A$ block of mass $10 \ kg$ is moving on a rough surface with a velocity $v = 4 \ m/s$ to the left. An external force $F = 20 \ N$ is applied to the right as shown in the figure. The coefficient of kinetic friction is $\mu = 0.6$. The frictional force acting on the block is ...... $N$.

Two blocks $A$ and $B$ of masses $2 \ kg$ and $4 \ kg$ respectively are kept on a rough horizontal surface. If the same force of $20 \ N$ is applied on each block,then the ratio of the accelerations of the blocks $A$ and $B$ is (Coefficient of kinetic friction between the surface and the blocks is $0.3$ and acceleration due to gravity $= 10 \ m \ s^{-2}$).

What is the angle between the instantaneous velocity and the friction force of an object moving on a rough surface (in $^{\circ}$)?