The battery powers the motor that drives a paddle wheel to stir the gas at unifo

Question

The battery powers the motor that drives a paddle wheel to stir the gas at uniform pressure and temperature. The motor is diathermal and the tank containing the gas is also diathermal. The battery is adiabatic. Choose the battery as the system. Show the system from a thermodynamic point of view and the energy (rate) interactions between the system and the surrounding using proper arrows, and label them clearly, e.g., and . Overload the latter with appropriate subscripts. The battery operates at 110 Volts. What is the current drawn by the motor in amp? What is the rate of change of the battery internal energy in kW?

Explanation / Answer

Q in is the energy in..(lable the pipe going in the motor as Q) W in is the energy out (lable the pipe going out of the motor as W) ?U is the change in internal energy of motor (lable the heat going out into surrounding from motor as ?U) rate of change of motor internal energy =Qdot -Wdot power output from motor is Wdot input power is 1.2 times the power output ie 1.2*Wdot... as 20 % energy is wasted power input =1.2(Wdot) =VI =110I hence I =0.011Wdot since the walls of battery are adiabatic . rate of change of battery internal energy = -power input to motor= -1.2Wdot

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