Question

In a screw jack, the effort required to lower the load W is given by

(a) P = W tan (α – ɸ)

(b) P = W tan (α + ɸ)

(c) P = W tan (ɸ – α)

(d) P = W cos (α + ɸ)

This question was addressed to me in a job interview.

Origin of the question is Friction in Journal Bearing- Friction Circle in division Friction of Machine Kinematics

Answer 1

The correct answer is (c) P = W tan (ɸ – α)

The best I can explain: The effort required at the circumference of the screw to lower the load W is given by

P = W tan (ɸ – α)

 The effort required at the circumference of the screw to lift the load W is given by

P = W tan (α + ɸ).