AQA A-Level Physics Paper 1, November 2020: Question 8

1 mark · Medium difficulty · Multiple Choice

Calculate the speed of an object of mass 0.03 kg whose kinetic energy equals the energy of a photon of energy 1 x 10^18 eV.

Practise this question

Question

Multiple choice question 08. A photon has energy of 1 x 10^18 eV. An object of mass 0.03 kg has kinetic energy equal to the energy of the photon. What is the speed of the object? Four options are given: A, 1 m s^-1; B, 3 m s^-1; C, 10 m s^-1; D, 30 m s^-1.
Question text

08 A photon has energy of 1 × 1018 eV.

An object of mass 0.03 kg has kinetic energy equal to the energy of the photon.

What is the speed of the object?

[1 mark]

A 1 m s−1

B 3 m s−1

C 10 m s−1

D 30 m s−1

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer is B for question 08.

08 B

How to answer it

Photon Energy to Kinetic Energy Conversion

What this question tests

This question assesses your ability to convert energy units from electronvolts (eV) to joules (J), equate photon energy to macroscopic kinetic energy, and rearrange the standard kinetic energy formula to solve for velocity. It tests fundamental unit conversion skills and algebraic rearrangement in a multiple-choice format.

Question 08 [1 Mark]

AQA A-Level Physics

Correct Answer: B (3 m s⁻¹)

✅ Correct Answer

Option B is correct because calculating the speed using properly converted joules yields exactly 3 m s⁻¹.

💡 Key Knowledge

  • Electronvolt Conversion: 1 eV = 1.60 × 10⁻¹⁹ J. Always multiply by the elementary charge to convert eV to Joules.
  • Kinetic Energy Formula: KE = 0.5 × m × v²

🧠 Exam Technique

For multiple-choice calculation questions, do a quick rough estimate or full calculation on your scratchpad before looking at the options to avoid falling into distractor traps set by powers of ten.

❌ Common Errors

  • Forgetting to convert electronvolts (eV) into joules (J).
  • Forgetting to square root the final velocity term (solving for v² instead of v).

📐 Step-by-Step Calculation

  1. Step 1: Convert photon energy to Joules
    E = 1 × 10¹⁸ eV = 1 × 10¹⁸ × 1.60 × 10⁻¹⁹ J = 0.16 J (using standard elementary charge e ≈ 1.60 × 10⁻¹⁹ C).
    Note: Exact data booklet value e = 1.60 × 10⁻¹⁹ C gives E = 0.1602 J.
  2. Step 2: Equate to Kinetic Energy
    KE = 0.5 × m × v² = 0.1602 J
  3. Step 3: Rearrange for velocity (v)
    v² = (2 × KE) / m
    v² = (2 × 0.1602 J) / 0.03 kg
    v² = 0.3204 / 0.03 = 10.68 m² s⁻²
  4. Step 4: Take the square root
    v = √(10.68) = 3.26 m s⁻¹ ≈ 3 m s⁻¹ (matching option B).

Topics

Physics · 3.2 Particles and radiation · 3.4 Mechanics and materials

Question and mark scheme from the AQA A-Level Physics examination, Paper 1, November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.