A 120-V motor has mechanical power output of 2.70 hp. It is 94.0% efficient in c

Question

A 120-V motor has mechanical power output of 2.70 hp. It is 94.0% 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 3.40 h of operation. (c) If the electric company charges $0.110/kWh, what does it cost to run the motor for 3.40 h?

Explanation / Answer

Note, the difference between electrical power > mechanical power is wasted as heat. Mechanical power: P_m = 2.8hp * 746 W/hp = 2088.8 W Electrical power: P_e = P/eff =2088.8/0.91 = 2295.385 W a) Current: P_e = V*I I = P_e/V = 2295.385/120 = 19.128 A b) E = P*t = 25616496.6 J

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