AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), 2023: Question 6

💡 Big ideas in this question

• Use v² − u² = 2as for a falling object.
• Velocity is a vector: it has magnitude and direction.
• In water, drag acts opposite to motion.
• Constant velocity means resultant force = 0.

🧠 Examiner insight

• Students often lose marks by choosing the wrong equation or not showing working.
• For vector questions, saying only “it gets faster” is not enough — you must mention direction too.
• In the water explanation, stronger answers describe the whole sequence: drag greater than weight → slows down → drag decreases → drag equals weight.

✅ Correct answer

Velocity = 12 m/s (to 2 significant figures)

📐 Calculation steps

1. Write down the known values:
   • u = 3.1 m/s
   • a = 9.8 m/s²
   • s = 6.3 m
2. Choose the equation without time:
   v² − u² = 2as
3. Substitute in the values:
   v² − 3.1² = 2 × 9.8 × 6.3
4. Rearrange:
   v² = 3.1² + (2 × 9.8 × 6.3)
5. Calculate:
   v = √(3.1² + (2 × 9.8 × 6.3))
   v = 11.5...
6. Round to 2 significant figures:
   v = 12 m/s

💡 Key knowledge

• u = initial velocity
• v = final velocity
• a = acceleration
• s = distance moved
• This stone is speeding up as it falls because gravity causes a downward acceleration.

❌ Common errors

• Using the wrong SUVAT equation.
• Forgetting to square u .
• Writing 11.5 m/s and not rounding to 2 significant figures.
• Using the height wrongly as a negative number when the question has already given consistent values.

🧠 Exam technique

Always show the formula first. The mark scheme awards method marks, so even if your arithmetic goes wrong later, you can still pick up marks for the correct physics. Also, the final accuracy mark here depends on using the correct equation and actually calculating a value for v .

✅ Correct answer

The magnitude (speed) of the velocity increases uniformly, and the direction remains constant downward.

💡 Key knowledge

• Velocity is a vector, so you must describe both size and direction.
• With no air resistance, the stone accelerates at a constant rate due to gravity.
• “Uniformly” means at a steady/constant rate.

🧠 Exam technique

Because the question starts with “Velocity is a vector”, that is a clear clue that one mark is for speed and one mark is for direction. Top answers include both explicitly.

❌ Common errors

• Saying only “it speeds up” — this misses the direction mark.
• Saying the direction changes — it does not, it stays downward.
• Talking about force instead of velocity.

✅ Correct answer

When the stone enters the water, drag is greater than its weight. This means there is a resultant force upwards, opposite to the direction of motion, so the stone decelerates. As the stone slows down, the drag decreases. Eventually, drag equals weight, so the resultant force is zero and the stone continues at a constant velocity.

💡 Key knowledge

• Weight acts downward.
• Drag (resistive force) acts opposite to motion, so upward here.
• If forces are unbalanced, the object accelerates or decelerates.
• If forces are balanced, resultant force is zero and velocity stays constant.

🧠 Exam technique

This is a chain-of-reasoning question. The best answers follow the order of events:

1. State which force is bigger at first.
2. Link this to a resultant force opposite the motion.
3. Say the stone slows down.
4. Explain that less speed means less drag.
5. Finish with equal forces and constant velocity.

Examiner commentary: students often got some marks for mentioning drag, but lost full marks by not explaining why the drag changes or by not stating that the resultant force becomes zero.

❌ Common errors

• Saying “weight decreases” — weight stays the same.
• Saying “constant velocity because drag is bigger than weight” — if drag is bigger, it is still slowing down.
• Missing the idea that drag decreases as speed decreases.
• Talking about acceleration being zero without linking it to balanced forces.

💡 Extra examiner note

The mark scheme says ignore upthrust, so you do not need to discuss buoyancy here. Focus on the two forces the mark scheme rewards: weight and drag.

✅ Part (06.1) model answer

Use v² − u² = 2as .
v² − 3.1² = 2 × 9.8 × 6.3
v = √(3.1² + (2 × 9.8 × 6.3)) = 11.5...
So the velocity is 12 m/s to 2 significant figures.

✅ Part (06.2) model answer

The speed increases uniformly and the direction stays constant downward.

✅ Part (06.3) model answer

In the water, drag is greater than the stone’s weight, so there is a resultant force upward, opposite to its motion. This makes the stone decelerate. As it slows down, the drag decreases until drag equals weight. The resultant force is then zero, so the stone continues at a constant velocity.

💡 Make sure you can...

• Select the correct SUVAT equation.
• Substitute values carefully with units.
• Round to the required significant figures.
• Describe vectors using magnitude and direction.
• Explain constant velocity using balanced forces.

🧠 How to secure full marks

• Show every step in calculations.
• Use key physics words: resultant force, deceleration, drag, constant velocity.
• For explanation questions, write in logical order.
• Answer exactly what the mark scheme rewards — no need for extra complicated ideas.