Question

In a screw jack, the effort required to lift 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 posed to me in a national level competition.

The question is from Friction in Journal Bearing- Friction Circle in division Friction of Machine Kinematics

Answer 1

The correct answer is (b) P = W tan (α + ɸ)

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

P = W tan (α + ɸ)

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

P = W tan (ɸ – α).