Let T be the net torque developed by the rotor runs at ω rad/s. What is the mechanical power developed?

• A. Pmech = (ωT)/60
• B. Pmech = ωT
• C. Pmech = (2πωT)
• D. Pmech = (2πωT)/60

Answer: (B)

By the term, torque is meant the turning or twisting moment of a force about an axis. It is measured by the product of the force and the radius at which this force acts. Consider a pulley of radius r meter acted upon by a circumferential force of F Newton which causes it to rotate at N r.p.m.
The angular speed of the pulley is
ω = 2πN/60 rad/sec
Work is done by this force in one revolution
= Force × distance = F × 2πR Joule
The power developed = Work Done/Time
= (F × 2πR)/60/N
= (F × R) × (2πN)/60
The power developed = T × ω watt or P = T ω Watt
pmech = (ωT)