Can you please have look at the attached file. I am having difficulty with Q6 part (v), not sure how to go about it! Torque constant, Kt = 0.8 Back e.m.f constant, Ke = 1.25 Any help is greatly appreciated.
You know Ke, thus The voltage developed across the motor terminals, without the 5 ohm resistor connected, is E=Ke*ω You know Ke and ω thus you can calculate E (which is actually the back EMF when it is working as a motor). The armature resistance is 5 ohms and the load resistance (connected on the motor terminals) is also 5 ohms. Thus the total resistance is 10 ohms. Thus the current through the armature and the load resistance is : I=E/10 Thus the power dissipated in the load is: P=(I^2)*5 Assuming no losses, the torque is: T=P/ω
The load resistance is just a resistor, 5 ohms in this case, which is connected across the terminals of the motor.