Two blocks, A and B (with mass 50 kg and 100 kg, respectively), are connected by
ID: 1907901 • Letter: T
Question
Two blocks, A and B (with mass 50 kg and 100 kg, respectively), are connected by a string, as shown in Figure P5.64. The pulley is frictionless and of negligible mass. The coefficient of kinetic friction between block A and the incline is ?k = 0.25. Determine the change in the kinetic energy of block A as it moves from C to D, a distance of 15 m up the incline if the system starts from rest. ____J
Explanation / Answer
assuming that A and B start from rest PE lost of B = 100 * g * 24 = 23544 J net force on the system mass = 100 g - 0.29 * 50 g cos 37 - 50 g sin 37 = 572.2 N acc of system mass = 572.2 / 150 = 3.81 m/s^2 u=0; a= 3.81 ; s =24 v^2 = u^2 + 2as v^2 = 0 + 2 * 3.81 * 24 v= 13.52 --speed of 100kg KE of 100kg = 0.5 * 100 * 13.52^2 = 9139.52J PE gain by A = 50 * g * 24 sin 37 friction force on A = 0.29 * 50 g cos 37 work done to overcome friction force = 0.29 * 50 g cos 37 * 24 conservation of energy 23544 = 50 * g * 24 sin 37 + 0.29 * 50 g cos 37 * 24 + the change in the kinetic energy of block A + 9139.52 the change in the kinetic energy of block A = 4593.46 J
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