When a body is moving on a surface,the force of friction is called

With what minimum velocity should a block be projected from the left end $A$ towards end $B$ such that it reaches the other end $B$ of a conveyor belt moving with a constant velocity $v$ towards the left? The length of the belt is $L$ and the coefficient of friction between the block and the belt is $\mu$.

$A$ block of mass $5\,kg$ is placed at rest on a table with a rough surface. If a force of $30\,N$ is applied parallel to the surface of the table,the block slides through a distance of $50\,m$ in $10\,s$. Calculate the coefficient of kinetic friction. (Given: $g = 10\,m/s^2$)

$A$ 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 $\,N$)

The blocks shown in the figure move with a constant velocity of $10 \, m/s$ towards the right. All surfaces in contact are rough. The friction force applied by the ground on block $B$ is ........ $N$.

Which of the following is correct when a person walks on a rough surface?