$A$ 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 $\,N$)

$A$ small box resting on one edge of the table is struck in such a way that it slides up to the other edge,$1 \, m$ away,after $2 \, s$. The coefficient of kinetic friction between the box and the table

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

$A$ horizontal force of $4\,N$ is needed to keep a block of mass $0.5\,kg$ sliding on a horizontal surface with a constant speed. The coefficient of sliding friction must be: $[g = 10\,m/s^2]$

$A$ block of mass $5 \,kg$ moving on a rough surface with a velocity of $4 \,ms^{-1}$ is stopped by friction in $2 \,s$. The coefficient of friction between the contact surfaces is (Acceleration due to gravity $g = 10 \,ms^{-2}$)

$A$ block is projected with speed $20 \,m/s$ on a rough horizontal surface. The coefficient of friction $(\mu)$ between the surfaces varies with time $(t)$ as shown in the figure. The speed of the body at the end of $4 \,s$ will be ............ $m/s$ $(g = 10 \,m/s^2)$.