If the mass of an object is doubled,what will be the effect on the coefficient of friction?

Which of the following is true about the coefficient of static friction $(\mu_s)$ and the coefficient of kinetic friction $(\mu_k)$?

$A$ 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.

$A$ pulling force $F$ making an angle $\theta$ with the horizontal is applied on a block of weight $W$ placed on a horizontal table. If the angle of friction is $\alpha$,then the magnitude of the force required to move the body is equal to

$A$ block placed on a rough horizontal surface is pulled by a horizontal force $F$. Let $f$ be the force applied by the rough surface on the block. Plot a graph of $f$ versus $F$.

As shown in the figure,a block of mass $\sqrt{3} \text{ kg}$ is kept on a horizontal rough surface with a coefficient of friction $\mu = \frac{1}{3 \sqrt{3}}$. $A$ force $F$ is applied on the vertical face of the block at an angle of $60^{\circ}$ with the horizontal. The minimum force $F$ required to just move the block is $3x$. Find the value of $3x$.
$\left[ g = 10 \text{ m/s}^2; \sin 60^{\circ} = \frac{\sqrt{3}}{2}; \cos 60^{\circ} = \frac{1}{2} \right]$