Theory of Machine
When the addenda on pinion and wheel is such that the path of approach and path of recess are half of their maximum possible values, then the length of the path of contact is given by (where r = Pitch circle radius of pinion, R = Pitch circle radius of wheel, and φ = Pressure angle)

[(r² + R²) cosφ]/2
[(r² + R²) sinφ]/2
[(r + R) cosφ]/2
[(r + R) sinφ]/2

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Theory of Machine
Power of a governor is the

Mean force exerted at the sleeve for maximum equilibrium speed
Mean force exerted at the sleeve for a given percentage change of speed
None of these
Work-done at the sleeve for maximum equilibrium speed

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