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

✅ Correct answers

• Vector quantity: has magnitude and direction
• Scalar quantity: has magnitude only

💡 Key knowledge

• Magnitude means size or amount.
• Examples of vectors: velocity, force, momentum.
• Examples of scalars: speed, distance, time, mass.

🧠 Exam technique

• Use the exact wording “magnitude and direction” for a vector.
• Use the exact wording “magnitude only” for a scalar.
• Keep it short: these are definition marks.

❌ Common errors

• Saying a vector has “size and speed” or “force and direction” only.
• Writing that a scalar has “no direction” without saying it has magnitude only.
• Confusing speed and velocity.

✅ Correct answers

• A resistive force acts on the ball.
• This force is in the opposite direction to the motion/velocity.
• Accept: friction or air resistance.
• Alternative mark point: work is done on the ball.

💡 Key knowledge

• When an object has a resultant force opposite its motion, it slows down.
• The lane is horizontal, so weight and normal contact force balance vertically.
• The slowing is caused by horizontal resistive forces.

🧠 Exam technique

• State the cause first: friction / air resistance.
• Then link it to motion: it acts opposite to velocity.
• Use the word decelerates or slows down.

❌ Common errors

• Saying “gravity slows it down” on a horizontal lane.
• Writing only “there is friction” without explaining direction.
• Using “force” with no clue that it is resistive/opposite.

✅ Correct answers

• momentum = mass × velocity
• p = mv

💡 Key knowledge

• Momentum is measured in kg m/s.
• Mass is in kg.
• Velocity is in m/s.

🧠 Exam technique

• Remember: p stands for momentum, not pressure here.
• If you write words, make sure they are in the right order: mass × velocity.

❌ Common errors

• Writing p = m/v or v = mp instead.
• Leaving out the multiplication sign or using the wrong symbols.

📐 Calculations: step-by-step

1. Use the equation p = mv
2. Substitute the values: 26 = m × 5.0
3. Rearrange: m = 26 ÷ 5.0
4. Calculate: m = 5.2
5. Write the unit: kg

Mass = 5.2 kg

✅ Correct answer

5.2 kg

🧠 Exam technique

• Always start by writing the formula.
• Show the rearrangement, not just the final answer.
• Keep the unit kg in your final answer.
• Use the given values exactly: 26 and 5.0.

❌ Common errors

• Dividing the wrong way round: 5.0 ÷ 26 .
• Writing the answer without units.
• Rounding badly: 5 is not as good as 5.2 here.
• Forgetting that momentum is mass × velocity, so mass must be momentum ÷ velocity.

✅ Correct answers

• Momentum is conserved in the collision, if there are no external forces.
• The pin gains momentum.
• So the ball must lose momentum, which means it slows down.
• Accept extra credit idea: the ball and pin exert equal and opposite forces on each other.

💡 Key knowledge

• In a closed system, total momentum before = total momentum after.
• During collision, momentum is transferred from the ball to the pin.
• Less momentum usually means lower velocity if mass stays the same.

🧠 Exam technique

• Use the phrase “momentum is conserved”.
• Then explain the transfer: pin gains, ball loses.
• Finish by linking loss of momentum to slowing down.

❌ Common errors

• Saying the ball slows because “it uses up momentum” — momentum is not used up.
• Claiming momentum disappears.
• Forgetting the pin’s momentum increases.
• Talking only about force, with no momentum explanation.

💡 What examiners wanted

• Precise definitions for vector and scalar.
• A clear resistive-force explanation for slowing down on the lane.
• Correct recall of p = mv .
• A calculation with rearrangement and unit.
• A momentum-transfer explanation for the collision.

🧠 How to score the marks

• Use the correct keywords: magnitude, direction, friction, momentum conserved.
• Write short, direct statements for definition questions.
• For calculations, show every step clearly.
• Always include units in the final answer.