Mechanical Comprehension Test Flashcards

A square-threaded screw has a pitch of 0.25 inches (advances 0.25 in per turn). If a 12-inch handle is used to turn it, what is the ideal mechanical advantage?

Answer: About 301

MA of a screw = 2π × handle length / pitch = 2π × 12 / 0.25 ≈ 301.

Which type of stress acts perpendicular to the cross-section of a structural member and tends to pull it apart?

Answer: Tensile stress

Tensile stress acts perpendicular to a cross-section in a pulling direction, stretching the material.

A centrifugal pump moves fluid by spinning an impeller. If the impeller's rotational speed doubles, by approximately what factor does the pump's pressure output increase?

Answer: 4 times

Pump affinity laws state that pressure (head) varies as the square of rotational speed: doubling speed quadruples pressure.

A weight hangs from two ropes attached to the ceiling. Rope A makes a 30° angle with the vertical and Rope B is vertical. Which rope carries more tension?

Answer: Rope A

The angled rope must support both its share of vertical load and provide a horizontal component, giving it greater total tension than the vertical rope.

A hydraulic press has an input cylinder with a 1-inch diameter and an output cylinder with a 5-inch diameter. If the input piston moves down 10 inches, how far does the output piston move?

Answer: 0.4 inches

Volume is conserved: π(0.5)²×10 = π(2.5)²×d, solving gives d = 10×(0.25/6.25) = 0.4 inches.

A car engine produces 200 ft-lbs of torque at 3000 RPM. What is the horsepower output?

Answer: About 114 HP

HP = (Torque × RPM) / 5252 = (200 × 3000) / 5252 ≈ 114 HP.

When a metal rod is heated, it expands. If both ends are rigidly fixed so it cannot expand, what type of internal stress develops?

Answer: Compressive stress

Thermal expansion is blocked, so the rod is effectively being compressed by the fixed walls, creating compressive stress.