A 120-V motor has mechanical power output of 3.00 hp. It is 80.0% efficient inco
ID: 1673076 • Letter: A
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