To use the principle of work and energy to determine characteristics of a mass b

Question

To use the principle of work and energy to determine characteristics of a mass being pulled up an incline and determine the power that must be supplied to the system when the efficiency of the input system is considered. As shown, a 64.0 kg crate is pulled up a (theta) = 55.0 (degrees) incline by a pulley and motor system. Initially at rest, the crate is pulled s = 4.75meters up the incline. Undergoing constant acceleration, the crate reaches a speed of 2.40m/s at the instant it has traveled this distance.

a) Considering the coefficient of kinetic friction, u = 0.15, determine the power that the motor must supply to the crate the instant the crate travels a distance of 4.75 m.

b) If the motor has an efficiency of E = 0.85 , what power must be supplied to the motor to raise the crate?

Explanation / Answer

from laws of motion (2.4)^2 = 2*(a - gsin55 - .15*gcos55)*4.75 a = 9.65 force from motor = 64*9.65 = 618.12 power = F.v = 618.12*2.4 = 1483.49 b) power = .85*1483.49 = 1260.97

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