Why rotor copper loss in induction motor doesn't change with slip
The power in R2/s is the sum of rotor copper losses plus electrical power converted to mechanical power. To look at both the losses and the mechanical power, you can divide R2 into to two parts, R2 and R2(1-s)/s. The rotor current is proportional to E2xR2/s, so the rotor current and the losses in the rotor are directly proportional to slip. The mechanical power developed in the rotor is also proportional to slip.