If the normal force is doubled,the coefficient of friction is

$A$ block of mass $m$ is pressed against a vertical surface by a spring of unstretched length $l$. The spring is compressed by a distance $d$ as shown in the figure. If the coefficient of friction between the block and the surface is $\mu$,choose the correct statement.

The coefficient of friction $\mu$ and the angle of friction $\lambda$ are related as

The limiting friction between two bodies in contact is independent of

The maximum value of the applied force $F$ such that the block as shown in the arrangement does not move is (Acceleration due to gravity, $g=10 \,ms^{-2}$) (in $\,N$)

$A$ horizontal force of $10 \, N$ is necessary to just hold a block stationary against a wall. The coefficient of friction between the block and the wall is $0.2$. The weight of the block is ........ $N$.