CAIE A-Level Physics AS 4.1 Turning Effects of Forces Questions

Practise analysing centres of gravity, moments, couples and torque with force diagrams, equilibrium calculations and stability from the weight’s line of action.

Exam points

calculate and interpret moments about a pivot, including the effect of perpendicular distance and the direction of a force
use the principle of moments to solve unknown forces, distances or weights in balanced beams and other rigid systems
explain and calculate the moment of a couple, distinguishing a couple from a single-force turning effect
locate or use the centre of gravity and assess stability from the line of action of the weight

Covered syllabus points

4.1.1—The weight of an object may be taken as acting at a single point known as 4.1.2—The moment of a force 4.1.3—A couple is a pair of forces that acts to produce rotation only 4.1.4—The torque of a couple

[Maximum number: 1]

What is the centre of gravity of an object?

the geometrical centre of the object

the point at which the weight of the object may be considered to act

the point on the object about which there is a zero net torque

the point where gravity acts on the object

[Maximum number: 1]

A uniform beam PQ rests horizontally on a support at point S .

Figure for Question 2 — CAIE A-Level Physics AS

A rope is attached at one end of the beam. The rope is at an angle of $60^{\circ}$ to the vertical and exerts a force F, in newtons, on the beam.

What is the moment, in Nm , of the force F about the point S ?