1) Explain why is fs less than or equal to us (coefficient of static friction)N?

2)Prove than tan ϑ is equal to uk (coefficient of kinetic friction) when a block slides down an incline with a constant speed. (use symbols, not numbers)

If the ϑ is the maximum angle of incline just before the block moves, what is us (coefficient of static friction) in terms of ϑ?

3)Suppose that a block were made to move up the inclined plane with uniform speed by suspending masses on a string over the pulley. Derive an equation for the coefficient of kinetic friction for this case in terms of suspended masses, the mass of the block, and the angle of decline. (Neglect any friction and mass effects of the pulley.)