A 120-V motor has mechanical power output of 4.00 hp. It is 86.0% efficient in c

Question

A 120-V motor has mechanical power output of 4.00 hp. It is 86.0% efficient in converting power that it takes in by electrical transmission into mechanical power.

(a) 28.9 Find the current in the motor.
Correct: Your answer is correct. A

(b) Find the energy delivered to the motor by electrical transmission in 3.80 h of operation.
MJ

(c) If the electric company charges $0.110/kWh, what does it cost to run the motor for 3.80 h?
$

Explanation / Answer

Note, the difference between electrical power > mechanical power is wasted as heat. Mechanical power: P_m = 4 hp * 746 W/hp = 2984 W Electrical power: P_e = P/eff =2984/0.86 = 3469.77 W a) Current: P_e = V*I I = P_e/V =3469.77/120 =28.9 A b) E = P*t = 3469.77*3.8*3600= 47466453.6 J c) 1000 wh - $0.110 3469.77 wh - 0.110*3469.77/1000 = $0.38 for 3.8 h = 0.38*3.8 = $1.444

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