AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2020: Question 7

8 marks · Standard Demand difficulty · Extended Answer

Explain why a kangaroo can jump higher as its speed increases and calculate the spring constant of a tendon modeled as a spring from energy transfer and extension data.

Practise this question

Question

The question page shows Question 07 about kangaroos and tendons. A photo labeled Figure 8 shows a kangaroo mid-jump, and the text explains that each leg has a tendon connected to a muscle and each tendon can be modelled as a spring; when a jumping kangaroo lands, the tendons stretch. Part 07.1 includes a sketch graph labeled Figure 9 with maximum tendon length on the y-axis and speed of kangaroo on the x-axis; the line slopes upward, and the student is asked to explain why a kangaroo can jump higher as its speed increases for 3 marks. Part 07.2 states that a kangaroo has a maximum gravitational potential energy of 770 J during one jump, that 14% of this is transferred to elastic potential energy in one tendon when it lands, that the tendon’s unstretched length is 35.0 cm and stretched length is 42.0 cm, and asks the student to calculate the spring constant in N/m for 5 marks.
Question text

07 Kangaroos are large animals that travel by jumping.

Figure 8 shows a kangaroo.

Figure 8

Each leg of a kangaroo has a tendon connected to a muscle. Each tendon can be

modelled as a spring.

When a jumping kangaroo lands on the ground, the tendons stretch.

07.1 Figure 9 shows a sketch graph of how the maximum tendon length during a jump

changes with the speed of the kangaroo.

Figure 9

Explain why a kangaroo can jump higher as its speed increases.

[3 marks]

*22* 24

07.2 A kangaroo has a maximum gravitational potential energy during one jump of 770 J

When the kangaroo lands on the ground 14% of the maximum gravitational potential

energy is transferred to elastic potential energy in one tendon.

The tendon has an unstretched length of 35.0 cm

When the kangaroo lands on the ground the tendon stretches to a length of 42.0 cm

Calculate the spring constant of the tendon.

[5 marks]

Spring constant = N/m

Mark scheme

Show the mark scheme The mark scheme is a table with columns for Question, Answers, Extra information, Mark, and AO/Spec. Ref. For 07.1, it awards one mark each for stating that maximum tendon extension increases as speed increases, that elastic potential energy increases or the elastic force increases, and that this energy is transferred to gravitational potential energy; the AO/spec reference shown is AO3 6.1.2.2. For 07.2, it gives method marks for calculating elastic energy as 770 multiplied by 0.14 to get 107.8 J, finding the extension as 0.070 m, substituting into 107.8 = 0.5 × k × 0.070 squared, rearranging to k = 2 × 107.8 divided by 0.070 squared, and obtaining k = 44 000 N/m; the AO/spec reference shown is AO2 6.1.1.2, and the total for the whole question is 8 marks.

AO /

Question Answers Extra information Mark

Spec. Ref.

07.1 the (maximum tendon) allow the tendons stretch more 1 AO3

extension increases (as speed (as speed increases) 6.1.2.2

increases)

so the elastic potential energy allow so the (elastic) force 1

increases increases

which is transferred to 1

gravitational potential energy

07.2 E = 770 × 0.14 allow E = 107.8 (J) 1 AO2

6.1.1.2

extension = 0.070m 1

107.8 = 0.5 × k × 0.0702 this mark may be awarded if 1

extension is incorrectly/not

converted and/or if the efficiency

equation has not been applied

107.8 this mark may be awarded if 1

k = 2 × 2

0.070 extension is incorrectly/not

converted and/or if the efficiency

equation has not been applied

k = 44 000 (N/m) this mark may be awarded if 1

extension is incorrectly/not

converted

this mark may not be awarded if

the efficiency equation has not

been applied

Total 8

How to answer it

Kangaroo tendons as springs

What this question tests
Understanding how increased speed affects tendon extension and elastic potential energy, plus using the spring energy equation E = 0.5 × k × e² correctly with unit conversion. You also need to explain a cause-and-effect chain clearly for full marks.

Question overview

This is a two-part GCSE physics question worth 8 marks in total: 07.1 is a 3-mark explanation, 07.2 is a 5-mark calculation.

Part 07.1 — Why can a kangaroo jump higher as its speed increases? [3 marks]

✅ Correct answer

  • The maximum tendon extension increases as speed increases.
  • This means more elastic potential energy is stored in the tendon.
  • That energy is then transferred to gravitational potential energy, so the kangaroo can jump higher.

💡 Key knowledge

  • A tendon can be modelled as a spring.
  • More extension = more energy stored in the spring.
  • When the tendon recoils, stored elastic energy can be transferred to movement and then to gravitational potential energy.

🧠 Exam technique

  • Use a chain of explanation: speed → extension → elastic potential energy → jump height.
  • To get full marks, make sure each step links logically to the next.
  • Short, clear physics statements are better than vague descriptions.

❌ Common errors

  • Saying only “it goes higher because it goes faster” without explaining why.
  • Mixing up elastic potential energy and gravitational potential energy.
  • Not mentioning that the tendon stretches more.
  • Using “force” alone without linking it to stored energy.

How the marks are awarded

  • 1 mark for saying the tendon extension increases as speed increases.
  • 1 mark for saying elastic potential energy increases.
  • 1 mark for saying this energy is transferred to gravitational potential energy.

Part 07.2 — Calculate the spring constant of the tendon [5 marks]

💡 Key knowledge

  • Use the spring energy equation: E = 0.5 × k × e²
  • E = elastic potential energy in joules (J)
  • k = spring constant in N/m
  • e = extension in metres (m)

🧠 Exam technique

  • Always convert cm to m before substituting into the equation.
  • Write the working clearly so you can pick up method marks.
  • Check that your final unit is N/m .

❌ Common traps

  • Using the full length of the tendon instead of the extension.
  • Forgetting to convert 7.0 cm into 0.070 m.
  • Using 770 J instead of 14% of 770 J.
  • Leaving the answer in the wrong unit.

📐 Calculation steps

  1. Find the elastic potential energy transferred to one tendon:
    E = 770 × 0.14 = 107.8 J
  2. Find the extension of the tendon:
    Unstretched length = 35.0 cm
    Stretched length = 42.0 cm
    extension = 42.0 - 35.0 = 7.0 cm = 0.070 m
  3. Substitute into the spring energy equation:
    107.8 = 0.5 × k × 0.070²
  4. Rearrange to find k :
    k = 2 × 107.8 / 0.070²
  5. Calculate:
    k = 43,959.18...
    So, to an appropriate number of significant figures:
    k = 44,000 N/m

✅ Final answer

Spring constant = 44,000 N/m

How the 5 marks are awarded

  • 1 mark for calculating the elastic potential energy: 770 × 0.14
  • 1 mark for finding the extension as 0.070 m
  • 1 mark for substituting into E = 0.5 × k × e²
  • 1 mark for rearranging correctly to find k
  • 1 mark for the correct final answer 44,000 N/m

❌ Calculation mistakes that lose marks

  • Using 35.0 cm or 42.0 cm directly in the equation instead of the extension.
  • Writing 7.0 m instead of 0.070 m .
  • Forgetting the factor of 0.5 in the spring equation.
  • Giving the answer without units.
  • Rounding too early in the working.

Top-mark answer model

How a full-mark 07.1 response could sound

As the kangaroo’s speed increases, the tendons stretch more. This means more elastic potential energy is stored in the tendon. The elastic energy is then transferred to gravitational potential energy, so the kangaroo can jump higher.

How a full-mark 07.2 response could sound

The energy transferred to one tendon is 770 × 0.14 = 107.8 J . The extension is 42.0 - 35.0 = 7.0 cm = 0.070 m . Using E = 0.5 × k × e² , 107.8 = 0.5 × k × 0.070² . Rearranging gives k = 2 × 107.8 / 0.070² = 44,000 N/m .

Topics

Physics · P1: Energy · P5: Forces

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Higher), 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.