Theory of Machine
The efficiency of a screw jack is maximum, when (where α = Helix angle, and φ = Angle of friction)

α = 45° + φ/2
α = 90° - φ
α = 45° - φ/2
α = 90° + φ

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Theory of Machine
Effort of a governor is the

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

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