$A$ block of mass $2 \ kg$ is placed on a rough horizontal surface. If a horizontal force of $20 \ N$ acting on the block produces an acceleration of $7 \ m \ s^{-2}$ in it,then the coefficient of kinetic friction between the block and the surface is $(g = 10 \ m \ s^{-2})$.

The coefficient of friction between the block and the surface is $0.03$. Find the acceleration of the system in $m/s^{2}$. $(g = 10\,m/s^{2})$

In the given figure,the acceleration of the block of mass $M = \frac{10}{3} \, kg$ is (given $g = 10 \, ms^{-2}$,$\mu = \frac{1}{3}$,$F = 50 \, N$,and $\theta = \sin^{-1}(\frac{3}{5})$):

$A$ small body of mass $500 \,g$ moves on a rough horizontal surface before finally stopping. The initial velocity of the body is $2 \,m/s$ and the coefficient of friction is $0.3$. Find the absolute value of the average power developed by the frictional force during the time of motion. (Take $g = 10 \,m/s^2$) (in $\,W$)

When two surfaces are coated with a lubricant,then they

$A$ block of mass $2 \,kg$ is being pushed against a wall by a force $F=90 \,N$ as shown in the figure. If the coefficient of friction is $0.25$, then the magnitude of acceleration of the block is (Take $g=10 \,ms^{-2}$, $\sin 37^{\circ}=\frac{3}{5}$). (in $\,ms^{-2}$)