The retarding acceleration of $7.35\, ms^{-2}$ due to frictional force stops a car of mass $400\, kg$ travelling on a road. The coefficient of friction between the tyre of the car and the road is

$A$ heavy box of mass $50 \,kg$ is moving on a horizontal surface. If the coefficient of kinetic friction between the box and the horizontal surface is $0.3$, then the force of kinetic friction is: (in $\,N$)

$A$ wooden block of mass $M$ resting on a rough horizontal surface is pulled with a force $F$ at an angle $\phi$ with the horizontal. If $\mu$ is the coefficient of kinetic friction between the block and the surface,then the acceleration of the block is:

$A$ 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 ...... $N$.

Consider a block and trolley system as shown in the figure. If the coefficient of kinetic friction between the trolley and the surface is $0.04$,the acceleration of the system in $m/s^2$ is (Consider that the string is massless and unstretchable and the pulley is also massless and frictionless):

Explain kinetic friction. Write the laws of kinetic friction. Define the coefficient of kinetic friction.