The coefficient of friction between the block of mass ${M_1}$ and the surface is $\mu$. When the system is released,it moves with acceleration. What mass $m$ should be placed on the block ${M_1}$ so that the system moves with a constant velocity?

$A$ lift is moving downwards with an acceleration equal to acceleration due to gravity. $A$ body of mass $M$ kept on the floor of the lift is pulled horizontally. If the coefficient of friction is $\mu$,what is the frictional resistance offered by the body when the lift is moving upwards with a uniform velocity?

$A$ block of mass $M$ is moving on a rough horizontal surface with momentum $P$. The coefficient of friction between the block and the surface is $\mu$. The distance covered by the block before it stops is $[g = \text{acceleration due to gravity}]$.

$A$ fireman of mass $60 \ kg$ slides down a pole. He is pressing the pole with a force of $600 \ N$. The coefficient of friction between the hands and the pole is $0.5$. With what acceleration (in $m/s^2$) will the fireman slide down? (Take $g = 10 \ m/s^2$)

$A$ boy of mass $40 \,kg$ is climbing a vertical pole at a constant speed. If the coefficient of friction between his palms and the pole is $0.8$ and $g = 10 \,m/s^2$, the horizontal force that he is applying on the pole is: (in $\,N$)

$A$ block of mass $\sqrt{2} \,kg$ is placed on a rough horizontal surface. $A$ force $F$ acting upwards at an angle of $45^{\circ}$ with the horizontal causes the block to start motion. If the coefficient of static friction between the surface and the block is $0.25$, the magnitude of the force $F$ is (Acceleration due to gravity $= 10 \,ms^{-2}$) (in $\,N$)