A 2.5 kg block is initially at rest on a horizontal surface. A
horizontal
force F of magnitude 6.0 N and a vertical force P are
then applied to the
block. The coefficients for friction for the block and the surface
are μs =
0.40 and μk = 0.25. Determine the magnitude of the frictional
force
acting on the block if the magnitude of P is (a) 8.0 N and (b)
12 N.