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A 120-V motor has mechanical power output of 3.20 hp. It is 81.0% efficient in converting power that it takes in by electrical transmission into mechanical power.
(a) Find the current in the motor.
Answer: 24.6A
(b) Find the energy delivered to the motor by electrical transmission in 3.60 h of operation.
(c) If the electric company charges $0.160/kWh, what does it cost to run the motor for 3.60 h?

  • physics -

    (b) Output power = 3.20 hp = 2387 Watts
    Input power = 2387/0.81 = 2947 W

    Electrical energy delivered in 3.60 h
    = 2947 J/s*3.2 h*3600 s/h = 3.395*10^7 J

    (c) 2.947 kW*3.2 h = ___ kWh
    Multiply that by the cost per kWh

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