Question

The efficiency of a screw jack is maximum, when

(a) α = 45º + φ/2

(b) α = 45º – φ/2

(c) α = 90º + φ

(d) α = 90º − φ

I have been asked this question in quiz.

The doubt is from Friction and Double Hooke’s Joint topic in section Friction of Machine Kinematics

Answer 1

Right choice is (b) α = 45º – φ/2

Best explanation: The efficiency of a screw jack is maximum when sin (2α + φ) is maximum, i.e. when

α = 45º – φ/2.