$A$ 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 $\,N$)

$A$ 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 ............ $m/s^2$ $(g = 10 \, m/s^2)$.

Two blocks of masses $M_1$ and $M_2$ are connected with a string passing over a pulley as shown in the figure. The block $M_1$ lies on a horizontal surface. The coefficient of friction between the block $M_1$ and the horizontal surface is $\mu$. What additional mass $m$ should be placed on the block $M_1$ so that the system does not accelerate?

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 $\theta = \sin^{-1}(\frac{3}{5})$):

$A$ block is thrown with a velocity of $2 \, m/s$ (relative to the ground) on a belt,which is moving with a velocity of $4 \, m/s$ in the opposite direction of the initial velocity of the block. If the block stops slipping on the belt after $4 \, s$ of throwing,then choose the correct statement$(s)$:

$A$ body is moving along a rough horizontal surface with an initial velocity $6\,m/s$. If the body comes to rest after travelling $9\,m$,then the coefficient of sliding friction will be