R14-5. The crate, having a weight of 50 lb, is hoisted by the pulley system and motor M. If the crate starts from rest and, by constant acceleration, attains a speed of 12 ft/s after rising 10 ft, determine the power that must be supplied to the motor at the instant s = 10 ft. The motor has an efficiency & 0.74. = M S Prob. R14-5

4 m M = (30t²) N•m F = 15t N. If the rod of negligible mass is subjected to a couple moment of M=29t2 N;M where t is the time in seconds, and the engine of the car supplies a braking force F= 15t N to the wheels, determine the speed of the car at t= 8s. The car at t=0s a a speed of 7 m/s. The total mass of the car and the driver is 158 kg. Neglect the size of the car.

15-51. The 30-Mg freight car A and 15-Mg freight car B are moving towards each other with the velocities shown. Determine the maximum compression of the spring mounted on car A. Neglect rolling resistance

14-59. The escalator steps move with a constant speed of 0.6 m/s. If the steps are 125 mm high and 250 mm in length, determine the power of a motor needed to lift an average mass of 150 kg per step. There are 32 steps. *14-60. If the escalator in Prob. 14–46 is not moving, determine the constant speed at which a man having a mass of 80 kg must walk up the steps to generate 100 W of power-the same amount that is needed to power a standard light bulb. 250 mm - 125 mm v = 0.6 m/s 4 m