CourseCourseConceptConceptDocsDocuments

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.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

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 as4.1.2—The moment of a force4.1.3—A couple is a pair of forces that acts to produce rotation only4.1.4—The torque of a couple

Question 1

[Maximum number: 1]

The cylinder in (a) is hung from the end A of a non-uniform bar AB , as shown in Fig. 3.1.

Fig. 3.1

Fig. 3.1

The bar has length 50 cm and has weight 0.25 N . The centre of gravity of the bar is 20 cm from B. The bar is pivoted at P. The pivot is 12 cm from B.

An object X is hung from end B. The weight of X is adjusted until the bar is horizontal and in equilibrium.

Explain what is meant by centre of gravity.

Question 2

[Maximum number: 2]

A pendulum consists of a solid sphere suspended by a string from a fixed point P , as shown in Fig. 3.1.

Fig. 3.1 (not to scale)

Fig. 3.1 (not to scale)

The sphere swings from side to side. At one instant the sphere is at its lowest position X , where it has kinetic energy 0.86 J and momentum 0.72 Ns in a horizontal direction. A short time later the sphere is at position Y , where it is momentarily stationary at a maximum vertical height h above position X.

The string has a fixed length and negligible weight. Air resistance is also negligible.

For the sphere at position Y , calculate the moment of its weight about point P .

moment =

Nm

Question 3

[Maximum number: 1]

Two forces act on an object.

Which diagram represents a couple?

Figure for Question 3 — CAIE A-Level Physics AS
Figure for Question 3 — CAIE A-Level Physics AS
Figure for Question 3 — CAIE A-Level Physics AS
Figure for Question 3 — CAIE A-Level Physics AS
A
Option A shown in diagram

Option A shown in diagram

B
Option B shown in diagram

Option B shown in diagram

C
Option C shown in diagram

Option C shown in diagram

D
Option D shown in diagram

Option D shown in diagram

All question bank results loaded