Question

The efficiency of a screw jack is given by

(a) tan (α + φ)/tan α

(b) tan α / tan (α + φ)

(c) tan (α − φ)/ tan α

(d) tan α/ tan (α − φ)

This question was addressed to me in class test.

I'd like to ask this question from Friction and Double Hooke’s Joint topic in portion Friction of Machine Kinematics

Answer 1

The correct answer is (b) tan α / tan (α + φ)

Easiest explanation: Efficiency, η = Ideal effort/ Actual effort

                           = P0 / P

                           = W tanα/ W tan(α + φ)

                           = tan α / tan (α + φ).