Block a in fig. 6-56 has mass ma 4.0 kg, and block b has mass mb 2.0 kg. the coefficient of kinetic friction between block b and the horizontal plane is mk 0.50.the inclined plane is frictionless and at angle u 30°. the pulley serves only to change the direction of the cord connecting the blocks. the cord has negligible mass. find (a) the tension in the cord and (b) the magnitude of the accel- eration of the blocks.