It is easier to roll a barrel than to pull it along the road. This statement is

$A$ block of mass $m$ is moving on a rough horizontal surface. The coefficient of kinetic friction between the block and the surface is $\mu_{k}$. The net force exerted by the surface on the block is (where $g$ is the acceleration due to gravity).

$A$ horizontal force of $40\,N$ is applied to a $5\,kg$ block which is at rest on a horizontal surface. If the coefficient of kinetic friction is $0.4$,then the acceleration of the block is ........ $m/s^2$ $(g = 10\,m/s^2)$.

$A$ block of mass $100 \ kg$ slides over a distance of $10 \ m$ on a horizontal surface. If the coefficient of friction between the surfaces is $0.4$,then the work done against friction (in $J$) is:

$A$ body of mass $20 \,kg$ is moving on a rough horizontal plane. $A$ block of mass $3 \,kg$ is connected to the $20 \,kg$ mass by a string of negligible mass through a smooth pulley as shown in the figure. The tension in the string is $27 \,N$. The coefficient of kinetic friction between the heavier mass and the surface is $\left(g=10 \,m/s^2\right)$.

$A$ car accelerates on a horizontal road due to the force exerted by: