Which is a suitable method to decrease friction

A pen of mass $m$ is lying on a piece of paper of mass $M$ placed on a rough table. If the coefficients of friction between the pen and paper and the paper and the table are $\mu_1$ and $\mu_2$, respectively. Then, the minimum horizontal force with which the paper has to be pulled for the pen to start slipping is given by

Explain -“Static friction force opposes impending motion”.

A body of mass $10$ kg slides along a rough horizontal surface. The coefficient of friction is $1/\sqrt 3 $. Taking $g = 10\,m/{s^2}$, the least force which acts at an angle of $30^o $ to the horizontal is ...... $N$

A block of mass $m$ rests on a rough inclined plane. The coefficient of friction between  the surface and the block is $\mu$. At what angle of inclination $\theta$ of the plane to  the horizontal will the block just start to slide down the plane?

A force acts on a block as shown in figure. Find time when block loses contact with surface.