Hello I don\'t really understand how to start question 40 in Chapter17 Here\'s t

Question

Hello I don't really understand how to start question 40 in Chapter17 Here's the question: A small motor draws a current of 1.75A from a 120-V line. Theoutput power of the motor is 0.20 hp. (a)At a rate of $0.060/kWh, what is thecost of operating the motor for 4.0h? (b) What is the efficiency of the motor? Hello I don't really understand how to start question 40 in Chapter17 Here's the question: A small motor draws a current of 1.75A from a 120-V line. Theoutput power of the motor is 0.20 hp. (a)At a rate of $0.060/kWh, what is thecost of operating the motor for 4.0h? (b) What is the efficiency of the motor? (b) What is the efficiency of the motor?

Explanation / Answer

To start make sure to remember the equation for power. P = Vi[Watts] This will give you a value with units of watts. From this you can do part a, by first finding the power supplied tothe motor from the line. Converting this answer to kW andremembering that watts are equivalent to a Joule/second you canconvert the power supplied to the line into kWh. Then multiply by0.060 and 4hours and you will get the cost. Part b is simply talking about the ratio between the power suppliedto the motor from the line, which you found in part a, and thepower the motor outputs, which is given as 0.2 hp.

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