static friction

Problem 509
The blocks shown in Fig. P-509 are connected by flexible, inextensible cords passing over frictionless pulleys. At A the coefficients of friction are μ_s = 0.30 and μ_k = 0.20 while at B they are μ_s = 0.40 and μ_k = 0.30. Compute the magnitude and direction of the friction force acting on each block.
 

Problem 508
The 200-lb block shown in Fig. P-508 has impending motion up the plane caused by the horizontal force of 400 lb. Determine the coefficient of static friction between the contact surfaces.