A) A 28.0-N block rests on a horizontal surface. The coefficients of static and kinetic friction between the surface and the block are ?s=0.890 and ?k=0.570. A horizontal string is attached to the block and a constant tension T is maintained in the string. What is the force of friction acting on the block if T = 23.92 N?
B) What is the force of friction acting on the block if T= 28.92 N?