Physics

Physics

Problem

A uniform horizontal beam is hinged at its left end (point A). Three forces act on the beam: • 15 N15\,\text{N} downward at 0.50 m0.50\,\text{m} from A. • 20 N20\,\text{N} upward at 1.00 m1.00\,\text{m} from A. • 25 N25\,\text{N} horizontally to the right applied exactly at A. Which of these forces produces zero torque about point A, and why?
Intuitive explanation

Torque measures how much a force tries to rotate an object around a pivot point—it depends on both the force's magnitude and its perpendicular distance from the pivot. Since point A is the hinge, any force applied directly at A has zero distance to the pivot, so it creates zero torque no matter how strong it is. The key insight is that only the horizontal force at A satisfies this condition.

Intuitive explanation

Torque measures how much a force tries to rotate an object around a pivot point—it depends on both the force's magnitude and its perpendicular distance from the pivot. Since point A is the hinge, any force applied directly at A has zero distance to the pivot, so it creates zero torque no matter how strong it is. The key insight is that only the horizontal force at A satisfies this condition.

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