Problem Assignment No. 3 Power and Efficiency 16 of 30 Learning Goal: To use the

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Problem Assignment No. 3

Power and Efficiency

16 of 30

Learning Goal:

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.

(Figure 1)

Part A - Power supplied to the crate when friction is considered

Considering the coefficient of kinetic friction, k = 0.11, determine the power that the motor must supply to the crate the instant the crate travels a distance of 5.1 m .

Express your answer to two significant figures and include the appropriate units.

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Part B - Power supplied to the motor when efficiency is considered

If the motor has an efficiency of = 0.87 , what power must be supplied to the motor to raise the crate?

Express your answer to two significant figures and include the appropriate units.

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1 of 1

Learning Goal:

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 50 kg crate is pulled up a = 45 incline by a pulley and motor system. Initially at rest, the crate is pulled s = 5.1 m up along the incline. Undergoing constant acceleration, the crate reaches a speed of 2.8 m/s at the instant it has traveled this distance.

(Figure 1)

Part A - Power supplied to the crate when friction is considered

Considering the coefficient of kinetic friction, k = 0.11, determine the power that the motor must supply to the crate the instant the crate travels a distance of 5.1 m .

Express your answer to two significant figures and include the appropriate units.

View Available Hint(s)

P=

Submit

Part B - Power supplied to the motor when efficiency is considered

If the motor has an efficiency of = 0.87 , what power must be supplied to the motor to raise the crate?

Express your answer to two significant figures and include the appropriate units.

View Available Hint(s)

P=

Submit

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Figure

1 of 1

Explanation / Answer

A) Power supplied, P = fk*v

= N*mue_k*v

= m*g*cos(45)*mue_k*v

= 50*9.8*cos(45)*0.11*2.8

= 107 W

B) P = m*g*cos(45)*mue_k*v

= 50*9.8*cos(45)*0.87*2.8

= 844 W

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