Question

The maximum efficiency of a screw jack is

(a) 1 – sinφ/ 1 + sinφ

(b) 1 + sinφ/ 1 – sinφ

(c) 1 – tanφ/ 1 + tanφ

(d) 1 + tanφ/ 1 – tanφ

This question was addressed to me in class test.

I would like to ask this question from Friction and Double Hooke’s Joint topic in section Friction of Machine Kinematics

Answer 1

Right choice is (a) 1 – sinφ/ 1 + sinφ

Best explanation: Maximum efficiency, ηmax = sin (90º – φ + φ) – sinφ/sin (90º – φ + φ) + sinφ

                                                 = sin 90º – sin φ/sin 90º + sin φ

                                                 = 1 – sinφ/ 1 + sinφ.