Allied & ICAR Exam Bank • ALLIED_1089 MCQ • 1 Mark

Section 2: Farm Machinery

Machine Design

Subtopic: Power Screws

Question Statement:

A square-threaded power screw is self-locking if its helix angle $\alpha$ and friction angle $\phi$ satisfy:

Options:

  • (A) \alpha \le \phi
  • (B) \alpha > \phi
  • (C) \alpha = 2\phi
  • (D) \alpha + \phi = 90^\circ

Answer Key:

A

Step-by-Step Solution & Explanation

A power screw is self-locking (cannot be reversed by load) when the friction angle equals or exceeds the helix angle, i.e., $\phi \ge \alpha$ or $\mu \ge \tan \alpha$.
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