AQA GCSE Physics Physics Paper 2 (Foundation), June 2025: Question 4

✅ Correct Answer

Tick box 3:

Car X has a smaller maximum acceleration.

💡 Key Knowledge

Rearrange Newton's Second Law: a = F / m .

Acceleration is inversely proportional to mass when resultant force is constant. Since Car X has a greater mass, it experiences a smaller acceleration for the same forward force.

📐 Step-by-Step Calculation

1. Identify given values:
   Mass, m = 900 kg
   Acceleration, a = 2.5 m/s²
2. Substitute into formula:
   F = 900 × 2.5
3. Calculate final value:
   F = 2250 N (or 2300 N to 2 sig figs)

❌ Common Errors

• Dividing mass by acceleration ( 900 / 2.5 ) instead of multiplying.
• Forgetting to write down the substitution step—always show your working to secure the method mark if an arithmetic slip occurs.

✅ Model Answer (Level 2, 4 Marks)

• Initially, the forward driving force is greater than air resistance, producing a forward resultant force that causes the car to accelerate.
• As the speed of the car increases, air resistance increases.
• Because air resistance opposes motion, the resultant force decreases, meaning the rate of acceleration decreases.
• Eventually, air resistance increases until it is equal in size to the maximum driving force.
• At this point, the resultant force becomes zero, and the car moves at a constant maximum speed.

🧠 Exam Technique & Mark Scheme Criteria

Level 2 (3–4 marks): You must explain changes in both forces (driving force and air resistance) and logically connect them to resultant force and maximum speed.

Level 1 (1–2 marks): Mentioning forces simply (e.g. "air resistance goes up") without linking cause and effect.

✅ Correct Completions

04.4: The thinking distance is affected by the driver's reaction time.

04.5: The braking distance is the distance travelled by the car under the braking force.

💡 Key Knowledge

• Thinking distance = speed × reaction time (distance travelled before the driver physically hits the brakes).
• Braking distance = distance travelled while the brakes exert a decelerating force on the wheels.

📐 Step-by-Step Solution

1. Locate 100 km/h on the x-axis: Follow the vertical gridline upwards.
2. Read Thinking Distance (solid line):
   Thinking distance = 20 m
3. Read Braking Distance (dashed line):
   Braking distance = 60 m
4. Add values together:
   Stopping distance = 20 + 60 = 80 m

🧠 Exam Technique: Error Carried Forward

Even if you misread one of the curves (e.g. reading 62 m instead of 60 m), you can still gain the remaining 2 marks by correctly showing the addition step and final answer: Stopping Distance = Thinking Distance + Braking Distance .

✅ Correct Selections (Tick Two)

• ☑ The driver becoming tired
• ☑ Driving on a wet road

💡 Factor Breakdown

• Driver tired: Increases reaction time → increases thinking distance → increases stopping distance.
• Wet road: Reduces friction between tyres and tarmac → increases braking distance → increases stopping distance.
• New tyres / new brakes: Increase friction → reduce braking distance.
• Driving uphill: Gravity opposes motion → helps car decelerate faster → reduces braking distance.