AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), 2024: Question 6

Question 06 overview

A rocket reaches 40 km, then coasts higher, then returns with parachutes.

💡 Key knowledge

• Use v² = u² + 2as for constant acceleration.
• Weight depends on mass and gravitational field strength: W = mg .
• At maximum height, the rocket is still moving upwards before it starts to fall.
• Parachutes increase air resistance and reduce terminal velocity.

🧠 Exam technique

• Always convert km to m in physics calculations.
• State the equation first, then substitute numbers, then calculate.
• For explanation questions, link cause → effect → result.
• Use the wording from the physics ideas: force, resultant force, air resistance, terminal velocity.

❌ Common errors

• Using 40 instead of 40 000.
• Forgetting the rocket starts from rest, so u = 0 .
• Saying weight changes because “gravity changes” without mentioning altitude or mass.
• Mixing up mass and weight.

✅ Correct answer

Velocity = 720 m/s

Awarded marks for: correct distance conversion, correct equation, correct substitution/rearrangement, correct final answer.

📐 Calculations step-by-step

1. Convert height: 40 km = 40 000 m
2. Use the equation: v² = u² + 2as
3. Substitute values: u = 0 , a = 6.48 m/s² , s = 40 000 m
4. v² = 0² + 2 × 6.48 × 40 000
5. v² = 518 400
6. v = √518 400 = 720
7. Final answer with unit: 720 m/s

🧠 How marks are awarded

• 1 mark for using s = 40 000 .
• 1 mark for a correct equation/substitution.
• 1 mark for rearranging correctly.
• 1 mark for the final velocity.

❌ Calculation traps

• Leaving height as 40 instead of 40 000.
• Forgetting to square root the final value.
• Writing the answer without units.
• Using the wrong equation such as v = u + at when no time is given.

✅ Correct answer

Weight depends on mass and gravitational field strength.

As the rocket burned fuel, its mass decreased, so its weight decreased.

Alternatively, as it moved higher, gravitational field strength decreased, so weight decreased.

💡 Key knowledge

• W = mg
• Mass decreases when fuel is used up.
• Weight is a force, so it changes if mass or gravitational field strength changes.

🧠 Examiner insight

• Top answers did three things: named the relationship, identified the change, and concluded weight decreased.
• Simple “it got lighter” answers sometimes gained only partial credit unless linked to mass or gravity.

❌ Common errors

• Saying mass decreases because weight decreases — backwards reasoning.
• Talking only about “force” without naming weight.
• Saying weight changes because of speed.

✅ Correct answer

• Gravitational force acts on the rocket in the opposite direction to its motion.
• There are no forces upwards once the fuel has stopped burning.
• So the resultant force is towards the Earth, causing the rocket to decelerate.

💡 Key knowledge

• If the rocket is still moving upwards, gravity acts downwards.
• When the engine stops, thrust is removed.
• A force opposite to motion makes an object slow down.

🧠 What the best answers included

• They clearly stated the force direction.
• They identified that the resultant force is downward.
• They used the word decelerates or “slows down”.

❌ Common errors

• Saying “no forces act” — gravity still acts.
• Confusing speed with acceleration.
• Saying the rocket slows because it is “getting higher” with no force explanation.

✅ Correct answer

• Parachutes increase the effective area.
• This increases air resistance.
• So air resistance balances weight at a lower speed, meaning the terminal velocity is lower.

💡 Key knowledge

• Terminal velocity happens when resultant force is zero.
• With parachutes open, a larger surface area catches more air.
• More air resistance means the downward force is balanced sooner.

🧠 Diagram/description advice

• If you had to sketch it, draw a large parachute canopy above the module with many lines showing the straps.
• Show a big downward weight arrow and a big upward air resistance arrow.
• Label the arrows clearly; this is what examiners expect to see in force questions.

❌ Common errors

• Saying parachutes “reduce gravity”. They do not.
• Only saying “it slows down” without explaining air resistance.
• Forgetting that terminal velocity means forces are balanced.

06.1

v = 720 m/s

06.2

Weight decreases because mass decreases as fuel is burned, or because gravitational field strength decreases with height.

06.3

Gravity acts downward, there is no upward thrust, so the resultant force is downward and the rocket decelerates.

06.4

Parachutes increase effective area, increasing air resistance, so terminal velocity is lower because balance is reached at a lower speed.