Compute all parts of following problem:
Problem: The weight of the block in the drawing is 81.0 N. The coefficient of static friction between the block and the vertical wall is 0.480.
Part A: What minimum magnitude of the force is required to prevent the block from sliding down the wall? (Hint: The static frictional force exerted by the block is directed upward, parallel to the wall.)
Part B: What minimum force is required to start the block moving up the wall? (Hint: The static frictional force is now directed down the wall.)
Please give me an explanation for above problem.