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Units and Measurement
Question
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To maintain a rotor at a uniform angular speed of 200 rad s–1, an engine needs to transmit a torque of 180 Nm. What is the power required by the engine?
(Note: uniform angular velocity in the absence of friction implies zero torque. In practice, applied torque is needed to counter frictional torque). Assume that the engine is 100 % efficient. 

Answer

Given,
Angular speed of the rotor, ω = 200 rad/s
Torque required, τ = 180 Nm
The power of the rotor (P) is related to torque and angular speed by the relation, 
P = τω 
  = 180 × 200
  = 36 × 103 

  = 36 kW 
Hence, the power required by the engine is 36 kW. 

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