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DC motor questions, help/confirmation needed

1. I have a question set that im unsure with as I dont have the final answers

A DC motor is shunt wound and is supplied with 500V. The armature resistance is 1ohm and the field winding is 500ohm. The running torque is 100Nm and the motor takes 21A. Determine the speed of the motor,

My calculations so far are

Calculate armature resistance : I-If = 21 - (500/500) = 20A

calculate back EMF = V - IaRa = 500 - 20 = 480V

Power = V(emf) x Ia = 480 x 20 - 9600W

Speed = P/2 x pi x T = (9600 / 2 x pi x 100) x 60 (to convert to rpm) = 917 rpm

Is this correct?

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