When a body is lying on a rough inclined plane and does not move, the force of friction

A bag is gently dropped on a conveyor belt moving at a speed of $2\,m / s$. The coefficient of friction between the conveyor belt and bag is $0.4$ Initially, the bag slips on the belt before it stops due to friction. The distance travelled by the bag on the belt during slipping motion is $.....m$ [Take $g=10\,m / s ^{-2}$ ]

A heavy box is solid across a rough floor with an initial speed of $4 \,m / s$. It stops moving after $8$ seconds. If the average resisting force of friction is $10 \,N$, the mass of the box (in $kg$ ) is .....

A $60\, kg$ body is pushed with just enough force to start it moving across a floor and the same force continues to act afterwards. The coefficient of static friction and sliding friction are $0.5$ and $0.4$ respectively. The acceleration of the body is  ........ $m/{s^2}$

An insect crawls up a hemispherical surface very slowly. The coefficient of friction between the insect and the surface is $1/3$. If the line joining the centre of the hemispherical surface to the insect makes an angle $\alpha $ with the vertical, the maximum possible value of $\alpha $ so that the insect does not slip is given by

Which of the following is a self adjusting force?