   Chapter 17, Problem 61AP

Chapter
Section
Textbook Problem

A 120.-V motor has mechanical power output of 2.50 hp. It is 90.0% efficient in converting power that it takes in by electrical transmission into mechanical power. (a) Find the current in the motor. (b) Find the energy delivered to the motor by electrical transmission in 3.00 h of operation. (c) If the electric company charges \$0.110/kWh, what does it cost to run the motor for 3.00 h?

(a)

To determine
The current in the motor.

Explanation

Given Info: The voltage applied on the motor is 120V . The mechanical power output is 2.50hp . 90.0% is the efficiency of motor in converting electrical power to mechanical power.

Explanation:

Formula to calculate the current in motor is,

I=P(ΔV)η

• I is the current in the motor
• P is the output power
• ΔV is the applied voltage
• η is the efficiency of motor in converting electrical power to mechanical power,

Substitute 2.50hp for P , 120V for ΔV and 90.0% for η in the above equation to find I

I=(2

(b)

To determine
The energy delivered to motor during 3.00h of operation.

(c)

To determine
The cost to run motor for 3 hours.

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