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

 

Thanks for your help, very well explained.

 

Im not very sure what 'load resistance' is ?
If possible could you go to a bit more detail.

Thanks

 

The load resistance is just a resistor, 5 ohms in this case, which is connected across the terminals of the motor.

 

Thanks, great help!