AQA GCSE Combined Science: Trilogy Physics Paper 2 (Foundation), November 2021: Question 1

✅ Correct Answer

Tick the box for: Electrostatic force

💡 Key Knowledge

• Non-contact forces act at a distance without physical contact: gravity, electrostatic force, magnetic force.
• Contact forces require objects to physically touch: friction, tension, air resistance, normal contact force.

✅ Correct Answer

Tick the box for: The downward force is the same size as the upward force.

🧠 Exam Technique & Physics Insight

Newton's Third Law states that when two objects interact, they exert equal and opposite forces on each other. The downward push of the person on the scales equals the upward push of the scales on the person.

❌ Common Errors

Thinking the downward force must be greater because the person is pushing down or "weighs a lot". If one force were larger, the scales or the person would accelerate into the ground!

✅ Correct Answer

Tick the box for: Normal contact force

💡 Key Knowledge

• Normal contact force: The perpendicular push exerted by a solid surface supporting an object. "Normal" means at right angles (90°) to the surface.
• Weight: Acts downwards towards the centre of the Earth.
• Air resistance: Only acts when an object is moving through air.

📐 Step-by-Step Calculation

1. Identify the formula:
   W = m × g
2. Substitute the values:
   W = 55 kg × 9.8 N/kg [1 mark]
3. Calculate final answer:
   W = 539 N [1 mark]

Note: The mark scheme also allows rounding to 540 (2 sig figs).

❌ Common Errors & Traps

• Dividing instead of multiplying: Always follow the formula provided in the question.
• Omitting working: Always show substitution ( 55 × 9.8 ) to secure the method mark if a calculation error occurs.
• Mass vs Weight: Mass is in kilograms ( kg ); Weight is a force measured in newtons ( N ).

✅ Correct Answer

Tick the box for: The weight decreased.

💡 Key Knowledge

Since Weight = mass × g , weight is directly proportional to gravitational field strength ( g ).

• The question states g is weakest at the equator.
• A lower value of g means a lower value of weight.
• The person's mass remains constant, but their weight decreases.

❌ Misconception

Confusing mass and weight. Students often incorrectly choose "The weight remained the same", confusing weight with mass.

✅ Correct Answer

Tick the box for: Centre of mass

💡 Key Knowledge

The centre of mass of an object is the single point at which the entire mass (and therefore weight) of the object may be thought to act.

❌ Common Errors

Guessing "centre of weight" or "centre of force" — these are made-up distractor terms not used in GCSE physics.

📐 Step-by-Step Calculation

1. Identify forces and directions:
   Upward force = 1100 N
   Downward force = 800 N
2. Subtract opposing forces:
   1100 − 800 = 300
3. State final value:
   Resultant force = 300 N (upwards)

🧠 Exam Technique

When two forces act along the same line in opposite directions, the resultant force is found by subtracting the smaller force from the larger force. (If they acted in the same direction, you would add them).