Consider the system shown in Fig. P6.81. The rope and pulley have negligible mass, and the pulley is frictionless. The coefficient of kinetic friction between the 8.00-kg block and the tabletop is µk = 0.250. The blocks are released from rest. Use energy methods to calculate the speed of the 6.00-kg block after it has descended 1.50 m. Fig. P6.81

Solution 86P According to mass- energy theorem, the sum of kinetic energy of the whole system and the frictional force energy is equal to the potential energy. Therefore, the necessary condition is, Kinetic energy + Energy due to force of friction = Potential energy …..(1) Kinetic energy of the system is = 1 × (8 + 6) × v ( let v be the speed) 2 2 Kinetic energy = 7v …..(2) The force of friction is = k 8 × 9.8 N...