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March 26, 2017

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A small motor draws a current of 1.76 A from a 110 V line. The output power of the motor is 0.20 hp.
(a) At a rate of $0.060/kWh, what is the cost, in cents, of operating the motor for 4.0 h?
(b) What is the efficiency of the motor?

for (a) i am doing IV*hours*price and its coming up worng.
and for (b) i changed .2hp into Watts. and i got 149.2W.

im just not sure how to do this problem.

  • physics - ,

    Pin=VI=110 * 1.76=193.6W = 0.1936KW.

    a. C = $0.060/kwh * 0.1936kw * 4h =
    $0.0465 = 4.65 cents.

    b. Po = 0.2hp * 746W/hp = 149.2W.

    %Eff.=(Po/Pin)100%,
    %Eff.=(149.2/193.6)100% = 77.1

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