AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2018: Question 2

12 marks · Standard Demand difficulty · Extended Answer

Plan an experiment to determine the density of an irregular object, complete a bar chart of densities for plastics, and calculate the uncertainty from repeated density measurements.

Practise this question

Question

The question page contains three linked parts about density. Part 02.1 shows a line drawing of an irregular solid shaped like a chess knight and asks the student to plan an experiment to determine its density, worth 6 marks, with several lines for a written method. Part 02.2 gives Table 1 listing densities of five plastics in kilograms per cubic metre: acrylic 1200, nylon 1000, polyester 1380, polystyrene 1040 and PVC 1100; below this is an incomplete bar chart with acrylic and nylon already drawn, missing a y-axis scale and the bars for polyester, polystyrene and PVC, worth 4 marks. Part 02.3 gives Table 2 with three repeat density values for another plastic, 960, 1120 and 1040 kg/m^3, and asks for the uncertainty in the results, worth 2 marks.
Question text

02 A student wanted to determine the density of the irregular shaped object shown

in Figure 3

Figure 3

02.1 Plan an experiment that would allow the student to determine the density

of the object.

[6 marks]

02.2 Another student did a similar experiment.

He determined the density of five common plastic materials.

Table 1 shows the results.

Table 1

Plastic material Density in kg/m3

Acrylic 1200

Nylon 1000

Polyester 1380

Polystyrene 1040

PVC 1100

Figure 4 shows the results plotted in a bar chart.

Figure 4

Complete Figure 4

You should:

• Write the correct scale on the y-axis.

• Draw the bars for polyester, polystyrene and PVC.

[4 marks]

02.3 The student is given a piece of a different plastic material.

The student determined the density of the material three times.

Table 2 shows the results.

Table 2

Density in kg/m3

1 960

2 1120

3 1040

Determine the uncertainty in the student’s results.

[2 marks]

Uncertainty = kg/m3

Mark scheme

Show the mark scheme The mark scheme shows Question 02 split into parts 02.1, 02.2 and 02.3, all referenced to specification point 6.3.1.1. For 02.1, a level-based scheme awards 1 to 6 marks for a valid density method, with indicative points including measuring mass with a balance, finding volume by water displacement using a measuring cylinder or Eureka can, and calculating density as mass divided by volume. For 02.2, 2 marks are for correct y-axis values and 2 marks for bars drawn to the correct heights, with partial credit for two correct values or bars; for 02.3, the uncertainty is calculated as half the range, shown as (1120 minus 960) divided by 2 equals 80 kg per cubic metre, with 160 gaining 1 mark.

AO /

Question Answers Mark

Spec. Ref.

02.1 Level 3: The method would lead to the production of a valid 5–6 AO1

outcome. All key steps are identified and logically sequenced. 6.3.1.1

Level 2: The method would not necessarily lead to a valid 3–4

outcome. Most steps are identified, but the method is not fully

logically sequenced.

Level 1: The method would not lead to a valid outcome. Some 1–2

relevant steps are identified, but links are not made clear.

No relevant content 0

Indicative content

• measure mass

• use a top pan balance or scales

• part fill a measuring cylinder with water

• measure initial volume

• place object in water

• measure final volume

• volume of object = final volume − initial volume

• fill a displacement / eureka can with water

• water level with spout

• place object in water

• collect displaced water

• measuring cylinder used to determine volume of displaced water

• use of:

mass

density =

volume

AO /

Question Answers Extra information Mark

Spec. Ref.

02.2 all y-axis values correct allow 1 mark for two correct 2 AO2

(minimum of 3) values 6.3.1.1

all bars drawn to the correct allow 1 mark for two correct bars 2

height allow ± ½ small square

02.3 an answer of 80 scores 2 marks AO3

6.3.1.1

(1120 - 960) ignore + and / or − signs 1

3 an answer of 160 scores 1 mark 1 8

= 80 (kg/m )

Total 12

How to answer it

Density of an Irregular-Shaped Object

What this question tests
Measuring mass and volume of an irregular object, using displacement to find volume, using the density formula, reading a bar chart scale, and finding uncertainty from repeated results.
Overall focus: practical skills + data handling

This question is mainly about how to measure density of an irregular object and how to process results carefully. The examiner rewards methods that are clear, logical, and complete, plus correct graph reading and uncertainty.

Part (a) / 02.1 — Plan an experiment to determine the density of the object

6 marks — high-value method question

✅ Correct answer idea

  • Measure the mass of the object using a top-pan balance or scales.
  • Measure the volume of the irregular object by water displacement.
  • Part-fill a measuring cylinder with water and record the initial volume.
  • Place the object in the water so that it is fully submerged.
  • Record the final volume.
  • Calculate the object’s volume using volume = final volume − initial volume .
  • Calculate density using density = mass ÷ volume .

💡 Key knowledge

  • Density is mass per unit volume.
  • For an irregular object, you cannot easily measure volume with a ruler.
  • The displacement method is the standard GCSE answer.
  • You can also use a Eureka can / displacement can:
    • fill the can with water until it runs from the spout,
    • place a measuring cylinder under the spout,
    • submerge the object,
    • collect displaced water and measure its volume.

🧠 Exam technique

  • To reach the top level, the method must be logical and complete.
  • Include the order of steps, not just a list of equipment.
  • Say fully submerged or completely under water to show the volume reading is valid.
  • Make the final step explicit: use the formula to calculate density.
  • If using a Eureka can, mention the water level at the spout first.

❌ Common errors

  • Only saying “measure density” without explaining how.
  • Forgetting to measure the mass.
  • Writing “measure the volume” with no displacement method.
  • Not subtracting initial volume from final volume.
  • Using a method that would not work for an irregular shape, such as measuring length × width × height.
  • Leaving out the density formula, so the plan is incomplete.

📐 A full-mark method in exam style

  1. Measure the mass of the object using a top-pan balance.
  2. Part-fill a measuring cylinder with water and record the initial volume.
  3. Carefully place the object into the water so that it is fully submerged.
  4. Record the new final volume.
  5. Work out the volume of the object by subtracting: final volume − initial volume.
  6. Calculate density using: density = mass ÷ volume.

Mark scheme link: The examiner awards marks for key steps such as measuring mass, finding volume by displacement, and using the density formula. The highest responses are clear, sequenced, and would give a valid result.

Part (b) / 02.2 — Complete the bar chart

4 marks — graph reading and accurate plotting

💡 Key knowledge

  • The table gives the missing densities:
  • Polyester = 1380 kg/m³
  • Polystyrene = 1040 kg/m³
  • PVC = 1100 kg/m³

✅ Correct answers

  • Write a y-axis scale that includes values up to at least 1380 kg/m³.
  • The scale must have a minimum of 3 values on the y-axis.
  • Draw bars to the correct heights:
    • Polyester: 1380 kg/m³
    • Polystyrene: 1040 kg/m³
    • PVC: 1100 kg/m³

🧠 Exam technique

  • Choose a scale that uses the graph space sensibly.
  • Make sure equal intervals on the y-axis are equal in value.
  • Bars should start from the correct baseline.
  • Use a ruler and draw bars to the right height, not “approximately near”.
  • The mark scheme allows a small tolerance: about ± ½ small square.

❌ Common errors

  • Using a y-axis scale that does not reach the highest value.
  • Missing out values or labelling the scale unevenly.
  • Drawing bars too short or too tall.
  • Confusing the order of materials.
  • Joining bars together like a line graph instead of leaving gaps.

📐 Suggested scale for the y-axis

A sensible scale could be:

  • 0
  • 400
  • 800
  • 1200
  • 1600

or any other correct linear scale that includes all values, especially 1380 kg/m³.

Mark scheme link: One mark is for correct y-axis values, and one mark is for each correctly drawn bar set. Accuracy matters more than fancy presentation.

Part (c) / 02.3 — Determine the uncertainty in the results

2 marks — repeated measurements and range method

✅ Correct answer

The results are:

  • 960 kg/m³
  • 1120 kg/m³
  • 1040 kg/m³

Uncertainty = (highest − lowest) ÷ 2

(1120 − 960) ÷ 2 = 80 kg/m³

📐 Step-by-step calculation

  1. Identify the highest value: 1120 kg/m³
  2. Identify the lowest value: 960 kg/m³
  3. Find the range: 1120 − 960 = 160 kg/m³
  4. Halve the range: 160 ÷ 2 = 80 kg/m³
  5. Final answer: 80 kg/m³

🧠 Exam technique

  • For repeated results, uncertainty is often taken as half the range.
  • Always quote the unit: kg/m³.
  • Show the arithmetic clearly if possible, because the method mark is for the process as well as the answer.

❌ Common errors

  • Giving the range as the uncertainty instead of half the range.
  • Using the average instead of the uncertainty.
  • Forgetting units.
  • Not identifying the highest and lowest values correctly.

⚠️ Calculation trap to avoid

The mark scheme accepts 80 kg/m³ for full marks. It also notes that an answer of 160 only gains 1 mark, because that is the range, not the uncertainty.

Quick recap: what to remember for full marks

💡 Core facts

  • Density = mass ÷ volume
  • Irregular object volume = water displacement
  • Uncertainty from repeats = half the range

🧠 Best exam habits

  • Write methods in order.
  • Use correct units.
  • Be precise with graph scales and bar heights.
  • Show calculation steps clearly.

❌ Biggest mark-loss risks

  • Missing mass measurement in part (a).
  • Forgetting to subtract volumes.
  • Wrong bar chart scale.
  • Giving 160 kg/m³ instead of 80 kg/m³.

Topics

Physics · Required Practicals · P3: Particle Model of Matter · Physics Required Practicals

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Higher), 2018. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.