AQA GCSE Combined Science: Trilogy Physics Paper 2 (Foundation), November 2020: Question 4

📐 Step-by-Step Calculation

1. Identify coordinates: The line starts at (0, 0) and ends clearly at (50 s, 250 m).
2. Find the gradient:
   gradient = change in y ÷ change in x
   gradient = (250 − 0) ÷ (50 − 0) = 250 ÷ 50
3. Calculate value:
   Speed = 5.0 m/s (or 5 m/s )

✅ Mark Scheme Breakdown

• [1 mark]: Correct substitution into gradient formula, e.g. 250 / 50 or using any matching coordinates along the line (e.g. 100 / 20 ).
• [1 mark]: Final value of 5.0 (or 5 ).

🧠 Exam Technique

Always pick points that are easy to read from the grid. Using the full line from (0, 0) to the very end point (50, 250) gives the most reliable values and avoids misreading small grid squares.

❌ Common Errors

Inverting the fraction (doing 50 ÷ 250 = 0.2 ). Remember that on a distance-time graph, distance (m) is on the vertical y-axis and time (s) is on the horizontal x-axis: speed = distance ÷ time .

✅ Correct Answer

Tick (✔) the box next to: Gravitational force

💡 Key Knowledge

• Non-contact forces: Act without physical contact between objects. The three main examples at GCSE are gravity, magnetic force, and electrostatic force.
• Contact forces: Require objects to physically touch. Examples: air resistance, friction, normal contact force, and tension.

❌ Common Errors

Confusing air resistance as a non-contact force. Even though air is an invisible gas, the bicycle must physically collide with air particles to experience resistance, making it a contact force.

📐 Step-by-Step Calculation

1. Identify values from the question:
   Force, F = 30 N
   Distance, s = 250 m
2. Substitute into the equation:
   work done = 30 × 250
3. Calculate answer:
   work done = 7500
4. Select the correct unit:
   Work done is an energy transfer, measured in Joules ( J ).

✅ Mark Scheme Breakdown

• [1 mark]: Correct substitution: 30 × 250
• [1 mark]: Calculation value: 7500
• [1 mark]: Unit: J

❌ Common Errors

• Selecting kg (unit of mass) or m (unit of distance) instead of J .
• Dividing force by distance instead of multiplying. The question provides the formula, so follow it directly: force × distance .

✅ Correct Sentence Completions

• "As the bicycle moves, work is done against frictional forces." [1 mark]
• "There is no change in the cyclist’s kinetic store of energy." [1 mark]
• "There is a decrease in the cyclist’s chemical store of energy." [1 mark]

💡 Why These Answers Are Correct

• Frictional forces: The tyres and moving components push against ground friction and air drag.
• Kinetic store: The prompt explicitly states the bicycle travels at a constant speed. Since kinetic energy depends on speed ( E_k = 0.5 × m × v² ), constant speed means no change in kinetic energy!
• Chemical store: The cyclist's muscles burn glucose from food to produce pedalling force, steadily depleting their chemical energy store.

🧠 Exam Technique

Always re-read the context sentence: "The bicycle travels at a constant speed." This is your clue that kinetic energy cannot be changing, immediately solving the second blank.