A 120-V motor has mechanical power output of 3.00 hp. It is 80.0% efficient inco

Question

A 120-V motor has mechanical power output of 3.00 hp. It is 80.0% efficient inconverting power that it takes in by electrical transmission intomechanical power. (a) Find the current in the motor.

A
(b) Find the energy delivered to the motor by electricaltransmission in 3.20 h ofoperation.

J
(c) If the electric company charges $0.160/kWh, what does it costto run the motor for 3.20 h?
$ (a) Find the current in the motor.

A
(b) Find the energy delivered to the motor by electricaltransmission in 3.20 h ofoperation.

J
(c) If the electric company charges $0.160/kWh, what does it costto run the motor for 3.20 h?
$

Explanation / Answer

a) The current in the motor at 120 volts is this:
Power = VI; 2795.6 I = 120; I =23.3 Amps
b) power = force x time = 2236.5 x 3.2 hours x 60 min/hr x 60sec/min = 25.76 MJ That's 25.76E6 Joules
c) at 0.16 per kWh:
p = 2975.6 W * 3.2 hr /1000 (W/kW) = 9.52 kWh
cost = $0.16/kWh * 9.52 kWh = $1.52

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