AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), 2018: Question 3

7 marks · Standard Demand difficulty · Short Answer

Write the equation linking momentum, mass and velocity, calculate the mass of an ice skater from momentum and velocity, and explain the velocity changes in a collision using conservation of momentum.

Practise this question

Question

The question page shows Figure 5, a simple drawing of an ice skater labelled Skater A skating to the right. Part 03.1 asks for the equation linking mass, momentum and velocity for 1 mark. Part 03.2 states that Skater A travels at 3.2 m/s and has a momentum of 200 kg m/s, and asks the student to calculate the mass for 3 marks with a final answer line labelled 'Mass = ___ kg'. Part 03.3 says Skater A bumps into another skater, Skater B, who is stationary, and that they move off together in a straight line; it asks students to explain what happens to the velocity of each skater using conservation of momentum for 3 marks.
Question text

03 Figure 5 shows an ice skater, Skater A.

Figure 5

03.1 Write down the equation that links mass, momentum and velocity.

[1 mark]

03.2 Skater A travels with a velocity of 3.2 m/s and has a momentum of 200 kg m/s

Calculate the mass of Skater A.

[3 marks]

11 Mass = kg

03.3 Skater A bumps into another skater, Skater B. Skater B is stationary.

The skaters move off together in a straight line.

Explain what happens to the velocity of each of the skaters.

Use the idea of conservation of momentum.

[3 marks]

Mark scheme

Show the mark scheme The mark scheme is a table with rows for questions 03.1, 03.2 and 03.3, plus columns for answers, extra information, mark and AO/specification reference. For 03.1, the accepted answer is momentum = mass × velocity, with p = mv allowed, worth 1 mark. For 03.2, marks are awarded for substituting 200 = m × 3.2, rearranging to m = 200/3.2, and giving m = 63 kg, with 62.5 kg allowed and full marks for 63 kg. For 03.3, marks are for stating that total momentum before the collision equals total momentum after, and for explaining that Skater A's momentum and velocity decrease while Skater B's momentum and velocity increase, or equivalent statements that momentum is shared between them.

AO /

Question Answers Extra information Mark

Spec. Ref.

03.1 momentum = mass × velocity allow p = mv 1 AO1

6.5.5.1

03.2 an answer of 63 (kg) scores 3 AO2

marks 6.5.5.1

200 = m × 3.2 1

200 1

m =

3.2

m = 63 (kg) allow 62.5 (kg) 1

03.3 (total) momentum before 1 AO1

(collision) = (total) momentum 6.5.5.2

after (collision)

either

momentum of skater A allow (total) momentum is 1

decreases and momentum of shared between skater A and

skater B increases skater B

velocity of skater A decreases 1

and velocity of Skater B

increases

or

momentum of skater A

decreases and so velocity of

skater A decreases (1)

momentum of skater B

increases and so velocity of

skater B increases (1)

Total 7

How to answer it

Skater Momentum: Equation, Mass and Collision

What this question tests

This question checks whether you can recall the momentum equation, rearrange it to find mass, and explain what happens in a collision using conservation of momentum. You also need to use correct units and link changes in momentum to changes in velocity.

Overall focus: momentum in a simple collision

Question 03.1

Write down the equation that links mass, momentum and velocity.

✅ Correct answer

momentum = mass × velocity

Accept: p = mv

1 mark for the correct relationship.

💡 Key knowledge

  • Momentum is measured in kg m/s.
  • Mass is measured in kg.
  • Velocity is measured in m/s.

🧠 Exam technique

  • For a 1-mark recall question, write the equation clearly and exactly.
  • Either words or symbols are fine.

❌ Common errors

  • Writing force = mass × acceleration instead of momentum.
  • Using speed instead of velocity in the equation statement.
  • Leaving out the × sign or writing the variables in the wrong order without clarity.

Question 03.2

Skater A travels with a velocity of 3.2 m/s and has a momentum of 200 kg m/s. Calculate the mass of Skater A.

📐 Calculations: step by step

  1. Start with the momentum equation: p = mv
  2. Substitute the values: 200 = m × 3.2
  3. Rearrange to find mass: m = 200 ÷ 3.2
  4. Calculate: m = 62.5 kg
  5. Round appropriately: 63 kg
The mark scheme allows 63 kg or 62.5 kg.

✅ Correct answer

Mass = 63 kg

Also accepted: 62.5 kg

3 marks: 1 for substitution, 1 for rearrangement, 1 for final answer.

💡 Key knowledge

  • Momentum = mass × velocity
  • To find mass, use mass = momentum ÷ velocity
  • Units matter: momentum in kg m/s, velocity in m/s, mass in kg.

🧠 Exam technique

  • Show working to access all 3 marks.
  • Write the equation first, then substitute numbers, then rearrange.
  • Keep units with your final answer.
  • Top responses clearly showed each stage, not just the final number.

❌ Common errors

  • Dividing the wrong way round, e.g. 3.2 ÷ 200.
  • Forgetting to rearrange before calculating.
  • Writing the answer with no unit.
  • Rounding too early and losing accuracy.

Question 03.3

Skater A bumps into stationary Skater B. The skaters move off together in a straight line. Explain what happens to the velocity of each skater. Use conservation of momentum.

✅ Correct answer

The total momentum before the collision equals the total momentum after the collision. Skater A’s momentum decreases, so Skater A slows down. Skater B was stationary, so its momentum increases and Skater B speeds up. Since they move off together, they travel with the same final velocity.

Marking idea: one mark for conservation of momentum, one for A slowing down, one for B speeding up / shared velocity.

💡 Key knowledge

  • Conservation of momentum: total momentum before = total momentum after.
  • If skaters stick together or move together, they share the same velocity after the collision.
  • Momentum is shared between the two skaters.

🧠 Exam technique

  • Use the phrase “total momentum before = total momentum after” to secure the key idea.
  • Then describe each skater separately.
  • A top-level answer links momentum changes directly to velocity changes:
    • Skater A slows down because momentum decreases.
    • Skater B speeds up because momentum increases.

❌ Common errors

  • Saying momentum is “lost” in the collision.
  • Forgetting that Skater B starts stationary.
  • Saying both skaters keep the same original velocity.
  • Not mentioning that they move off together, so they have the same final velocity.

📐 Extra exam insight

The mark scheme accepted two styles of explanation:

  • Style 1: total momentum before = total momentum after, then explain that A decreases and B increases.
  • Style 2: explain directly that A slows down and B speeds up because momentum is transferred/shared.

Students lost marks when they gave only vague statements such as “they both change speed” without saying how.

Full-mark recap

💡 Must-know facts

  • p = mv
  • momentum = mass × velocity
  • total momentum before = total momentum after in a closed system

🧠 How marks were awarded

  • 03.1: 1 mark for the correct equation.
  • 03.2: 3 marks for correct substitution, rearrangement, and answer.
  • 03.3: 3 marks for conservation of momentum plus correct velocity changes for both skaters.

❌ Final traps to avoid

  • Mixing up momentum with force.
  • Forgetting units in the calculation.
  • Not explaining both skaters in part 03.3.
  • Missing the fact that they move off together.

Topics

Physics · P5: Forces

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 2 (Higher), 2018. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.