A 120-V motor has mechanical power output of 2.10 hp. It is 80.0% efficient in c

Question

A 120-V motor has mechanical power output of 2.10 hp. It is 80.0% efficient in convertingpower that it takes in by electrical transmission into mechanicalpower. (a) Find the current in the motor.
1 A
(b) Find the energy delivered to the motor by electricaltransmission in 2.50 h of operation.
2 J
(c) If the electric company charges $0.160/kWh, what does it costto run the motor for 2.50 h?
$ 3 (a) Find the current in the motor.
1 A
(b) Find the energy delivered to the motor by electricaltransmission in 2.50 h of operation.
2 J
(c) If the electric company charges $0.160/kWh, what does it costto run the motor for 2.50 h?
$ 3

Explanation / Answer

We know that 1 hp = 746W Since Pout = 2.10 x 746= 1567 W Pin = Pout / efficiency = 1567 / 0.80=1958W a) Find the current in themotor.
Since P=VI I=P/V= 1958 / 120 I=16.3A
(b) Find the energy delivered to the motor byelectrical transmission in 2.50 h of operation.
E= Pint= 1958 x 2.5 x 3600 = E= 17.6 x106 J or E= 17.6 MJ (c) If the electric company charges$0.160/kWh, what does it cost to run the motor for 2.50h?
E= Pin t=1958 x 2.5= 4896W or 4.896kW $=E x rate $=4.896 x 0.160 $ = $0.783

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