IGCSE Physics Centre of Gravity Questions and Worked Solutions (1.5.3) | 0625

By /
IGCSE Physics 0625 · Topic 1.5.3

IGCSE Physics Centre of Gravity Questions and Worked Solutions

50 topic-wise practice questions on Centre of Gravity (Unit 1: Motion, Forces and Energy), written to the Cambridge IGCSE Physics 0625 syllabus for 2026–2028, each with a step-by-step worked solution.

50 questions40 Core0 Extended10 Challenge111 marksTextbook §1.5 · pp. 33–54
Questions tagged Core are for all candidates (Papers 1 & 3). Questions tagged Extended are Supplement content (Papers 2 & 4). Questions 41–50 are harder Challenge questions. Try each question first, then tap Show solution to check your working.

Topic guide: Centre of Gravity

The centre of gravity is the point through which the whole weight of an object seems to act. Its position decides how stable an object is and whether it will topple.

Key formulas

an object topples when its weight acts outside its baseline of action of the weightCore

Prerequisite knowledge

  • Weight (1.3)
  • Moments (1.5.2)

Exam tips & common mistakes

  • Explain toppling using the line of action of the weight relative to the edge of the base
  • In the plumb-line experiment, mention letting the lamina hang freely and come to rest
  • State BOTH low centre of gravity AND wide base for stability marks

Key facts from the syllabus (1.5.3)

  • The centre of gravity of a uniform regular shape is at its geometric centre
  • Find the centre of gravity of a plane lamina by hanging it from two points with a plumb line; it lies where the lines cross
  • An object is more stable if it has a low centre of gravity and a wide base
  • When tilted, an object returns to its original position if the weight still acts inside the base
  • The centre of gravity can lie outside the material (e.g. a ring)

Textbook: §1.5 Forces, pp. 33–54

1
Core[1 mark]

State what is meant by the centre of gravity of an object.

Show solutionHide solution

Method: The single point where weight can be taken to act.

The point through which the whole weight of the object appears to act
2
Core[1 mark]

State where the centre of gravity of a uniform metre rule is.

Show solutionHide solution

Method: Uniform: at the middle.

At the 50 cm mark (its centre)
3
Core[4 marks]

Describe an experiment to find the centre of gravity of an irregularly shaped plane lamina.

Show solutionHide solution

Method: Plumb line method.

Hang the lamina freely from a pin, hang a plumb line from the pin and mark the vertical line; repeat from a second hole; the centre of gravity is where the lines cross
4
Core[1 mark]

In the plumb-line experiment, explain why the lamina is hung from at least two points.

Show solutionHide solution

Method: One line only shows that the centre of gravity lies on it.

Two lines are needed so their intersection locates the centre of gravity
5
Core[1 mark]

State one precaution in the plumb-line experiment.

Show solutionHide solution

Method: Lamina must swing freely.

Make sure the lamina swings freely and is at rest before marking the line
6
Core[2 marks]

State two ways of making an object more stable.

Show solutionHide solution

Method: Low centre of gravity, wide base.

Lower its centre of gravity; widen its base
7
Core[2 marks]

Explain why racing cars are built low and wide.

Show solutionHide solution

Method: Low centre of gravity and wide base make toppling harder.

Low centre of gravity and wide base make them more stable when cornering
8
Core[2 marks]

Explain why a tall, narrow bottle topples more easily than a short, wide one.

Show solutionHide solution

Method: Its centre of gravity is high and its base is narrow.

High centre of gravity and narrow base: small tilt moves the line of action of the weight outside the base
9
Core[2 marks]

State the condition at which an object starts to topple over.

Show solutionHide solution

Method: Line of action of weight passes outside base.

When the vertical line through the centre of gravity falls outside the base
10
Core[2 marks]

A double-decker bus is loaded with passengers on the upper deck only. Explain why it is less stable than when the passengers sit on the lower deck.

Show solutionHide solution

Method: Mass high up raises the centre of gravity.

The centre of gravity is higher, so a smaller tilt moves the line of action of the weight outside the wheelbase
11
Core[1 mark]

State where the centre of gravity of a uniform rectangular sheet is.

Show solutionHide solution

Method: Symmetry.

Where the diagonals cross (its centre)
12
Core[2 marks]

Four identical blocks: 4 cm × 3 cm × 3 cm stood on a 3 × 3 face, and 6 × 3 × 2 cm laid on a 6 × 3 face. State which is more stable and why.

Show solutionHide solution

Method: Compare centre of gravity height and base area.

The block on the 6 × 3 face: lower centre of gravity and larger base
13
Core[2 marks]

Explain why a mountaineer leans forward when carrying a heavy backpack.

Show solutionHide solution

Method: Keeps combined centre of gravity above the feet.

To keep the combined centre of gravity above the feet (the base) so they do not fall backwards
14
Core[1 mark]

Explain why a table lamp has a heavy base.

Show solutionHide solution

Method: Heavy base lowers the centre of gravity.

It lowers the centre of gravity, making it more stable
15
Core[2 marks]

A Bunsen burner has a wide, heavy base. Give two reasons it is hard to knock over.

Show solutionHide solution

Method: Low centre of gravity and wide base.

Low centre of gravity; wide base area
16
Core[2 marks]

A ring-shaped lamina has its centre of gravity at the centre of the hole. Explain how this is possible.

Show solutionHide solution

Method: Centre of gravity need not be on the material.

The centre of gravity is a point where the weight appears to act; it can be outside the material by symmetry
17
Core[1 mark]

State what happens to an object if its centre of gravity is directly above its pivot.

Show solutionHide solution

Method: It is balanced (but may be unstable).

It is balanced (no moment from its weight)
18
Core[2 marks]

A ladder leans against a wall. A painter climbs higher. Explain the effect on stability.

Show solutionHide solution

Method: Combined centre of gravity rises.

Combined centre of gravity rises, so the ladder becomes less stable
19
Core[2 marks]

Explain why a wide-based glass is less likely to spill than a tall thin one when knocked.

Show solutionHide solution

Method: Line of weight stays within base longer.

Larger base and lower centre of gravity: it can tilt further before the weight acts outside the base
20
Core[2 marks]

A uniform plank is supported at one end only. Explain why it rotates.

Show solutionHide solution

Method: Its weight acts at the centre, creating an unbalanced moment.

Its weight acts at its centre of gravity, which is not above the support, so there is a resultant moment
21
Core[2 marks]

Describe the position of the centre of gravity of a uniform circular disc.

Show solutionHide solution

Method: Symmetry.

At the centre of the disc
22
Core[2 marks]

State why a plumb line is used when finding the centre of gravity of a lamina.

Show solutionHide solution

Method: Shows vertical.

It shows the vertical line through the point of suspension, which passes through the centre of gravity
23
Core[2 marks]

A lamina hanging from a pin comes to rest. State where its centre of gravity is relative to the pin.

Show solutionHide solution

Method: Directly below.

Directly below the pin
24
Core[2 marks]

Explain why a lorry carrying a heavy load high up is more likely to tip over on a bend.

Show solutionHide solution

Method: High centre of gravity.

Its centre of gravity is high, so a smaller tilt makes the line of action of the weight fall outside the wheelbase
25
Core[2 marks]

Explain why a baby's high chair has legs that spread outwards.

Show solutionHide solution

Method: Wide base.

A wider base makes it more stable
26
Core[2 marks]

State what happens to a tilted object if its weight acts inside the base when released.

Show solutionHide solution

Method: Returns.

It falls back to its original position
27
Core[2 marks]

State what happens to a tilted object if its weight acts outside the base when released.

Show solutionHide solution

Method: Topples.

It topples over
28
Core[2 marks]

Explain why a tightrope walker uses a long pole.

Show solutionHide solution

Method: Lowers centre of gravity / balance.

It helps lower the centre of gravity and makes it easier to keep it over the rope
29
Core[2 marks]

Explain why heavy items should be placed on lower shelves of a bookcase.

Show solutionHide solution

Method: Lower centre of gravity.

It keeps the centre of gravity low, making the bookcase more stable
30
Core[2 marks]

A cone stands on its base, then on its point, then on its side. State which position is most stable and explain.

Show solutionHide solution

Method: Low centre of gravity, wide base.

On its base: low centre of gravity and wide base
31
Core[2 marks]

Explain why a person standing with feet apart is more stable than with feet together.

Show solutionHide solution

Method: Wider base.

The base area is wider, so the weight must move further before it acts outside the base
32
Core[2 marks]

A uniform ruler balances on a finger at the 50 cm mark. A coin is placed at the 90 cm mark. State where the finger must be moved to balance it again.

Show solutionHide solution

Method: Towards the coin.

Towards the 90 cm end (between 50 cm and 90 cm)
33
Core[2 marks]

Explain why a full glass is more stable than an empty glass of the same type.

Show solutionHide solution

Method: Water lowers centre of gravity.

The water adds mass low down, lowering the centre of gravity relative to its height (and increasing weight)
34
Core[1 mark]

State the effect of adding a heavy mass to the base of a toy on its centre of gravity.

Show solutionHide solution

Method: Lowers it.

It lowers the centre of gravity
35
Core[3 marks]

A rectangular block 10 cm tall, with a base 4 cm wide, has its centre of gravity at its centre. Explain why it topples when tilted beyond a certain angle.

Show solutionHide solution

Method: Weight passes outside base edge.

When tilted, once the vertical line through the centre of gravity passes beyond the pivoting edge, the weight produces a moment that turns it over
36
Core[2 marks]

A filing cabinet has all its heavy files in the top drawer. Explain why it may tip over when that drawer is pulled out.

Show solutionHide solution

Method: Centre of gravity moves forward.

The centre of gravity moves forward and up; its line of action can fall outside the base, so it topples
37
Core[2 marks]

Explain why a pencil cannot be balanced on its point for long.

Show solutionHide solution

Method: Tiny base.

Its base is extremely small, so any small tilt moves its centre of gravity outside the base
38
Core[2 marks]

State one way of finding the centre of gravity of a uniform metre rule experimentally.

Show solutionHide solution

Method: Balance on knife edge.

Balance it on a knife edge (or finger) and find the point where it balances
39
Core[2 marks]

Explain why the centre of gravity of an L-shaped lamina can lie outside the material.

Show solutionHide solution

Method: Shape.

The mass is distributed so that the balance point lies in the empty corner region
40
Core[2 marks]

Explain why bus manufacturers carry out tilt tests.

Show solutionHide solution

Method: Check stability.

To check that the centre of gravity is low enough that the bus does not topple at a large tilt angle

Challenge questions

Harder, multi-step questions at the top end of the exam. Attempt these once you are confident with the questions above.

41
ChallengeCore[4 marks]

A lamina is hung from point A and a plumb line drawn; then from point B. Explain why the two lines cross at the centre of gravity, and how you would check the result.

Show solutionHide solution

Method: Weight acts vertically below suspension point.

When freely suspended, the centre of gravity is vertically below the pivot, so it lies on each line; it must be where they cross. Check by hanging from a third point — the third line should pass through the same point
42
ChallengeCore[4 marks]

A block 30 cm tall with a square base 10 cm wide has its centre of gravity at its centre. Explain why it topples when tilted about one edge by more than about 18°.

Show solutionHide solution

Method: tan θ = 5/15.

At about 18° (tan⁻¹(5/15)) the centre of gravity is directly above the edge; beyond this the weight's line of action falls outside the base and creates a toppling moment
43
ChallengeCore[4 marks]

Two identical bottles, one empty and one half-full of water, are tilted. Explain which one can be tilted further before toppling.

Show solutionHide solution

Method: Water lowers centre of gravity.

The half-full one: the water lowers its centre of gravity, so it must tilt further before the weight acts outside the base
44
ChallengeCore[3 marks]

Explain why a double-decker bus is designed with the engine and heavy parts low down, and why standing passengers are not allowed upstairs.

Show solutionHide solution

Method: Keep centre of gravity low.

Heavy parts low keep the centre of gravity low for stability; standing passengers upstairs would raise it, making the bus more likely to topple on bends
45
ChallengeCore[4 marks]

A uniform 1.0 m rule balances at 50 cm. A 20 g mass is taped at the 90 cm mark and the rule (mass 100 g) is re-balanced. Calculate the new balance point.

Show solutionHide solution

Method: Combined centre of gravity.

x = (100 × 50 + 20 × 90) ÷ 120 = 56.7 cm
46
ChallengeCore[3 marks]

Explain why a high-jumper using the Fosbury flop can clear a bar while their centre of gravity passes below it.

Show solutionHide solution

Method: Body bends around bar.

The body arches over the bar so different parts pass over at different times; the centre of gravity can lie outside the body, below the bar
47
ChallengeCore[4 marks]

A bookcase 2.0 m tall and 0.40 m deep has its centre of gravity 1.0 m high at the centre of its depth. Heavy books are placed on top, raising the centre of gravity to 1.4 m. Explain the effect on stability and calculate the tilt angle at which it would topple in each case.

Show solutionHide solution

Method: tan θ = 0.20 ÷ height of CG.

Before: 11.3°; after: 8.13° — it topples at a smaller angle so is less stable
48
ChallengeCore[3 marks]

Explain why a tall crane has a large counterweight close to the ground and a wide base.

Show solutionHide solution

Method: Stability.

These keep the combined centre of gravity low and over the base, so the line of action of the weight stays inside the base even with a load
49
ChallengeCore[3 marks]

Explain why it is hard to stand up from a chair without leaning forward first.

Show solutionHide solution

Method: Centre of gravity must be over feet.

Your centre of gravity is behind your feet when seated; leaning forward moves it over your feet (the new base) so you can stand without falling back
50
ChallengeCore[4 marks]

A rectangular sheet 40 cm × 20 cm has a 10 cm × 10 cm square cut from one corner. Explain qualitatively how the centre of gravity moves compared with the full sheet.

Show solutionHide solution

Method: Mass removed from one side.

It moves away from the cut corner, towards the opposite corner, because mass has been removed from that region
All IGCSE Physics topics← 1.5.2 Turning Effect of Forces1.6 Momentum →

Book a free trial class

Tell us a little about your requirement.