You can use that equation for AC or DC, for torque is mechanical by all means
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Power (watts) = 2xPixN(RPM)xT(N-m)/60(sec)
Therefore, T(N-m) = 9.548 P(watts)/N(RPM)
So, T(N-m) = 9548 P/N(RPM) if P is expressed in kW.
Regards,
Believe it or not : Had we trusted Archimedes and assigned him the work of lifting the earth(or any mass equivalent to that of earth on earth),with a lever of suitable length, it would have taken him 23 million million years to lift the earth by one centimeter.