AQA GCSE Physics Physics Paper 2 (Higher), November 2020: Question 5

Mark scheme

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Question 5

AO /

Question Answers Extra information Mark

Spec. Ref.

05.1 (total) momentum before = allow (total) momentum stays 1 AO1

(total) momentum after the same 4.5.7.2

05.2 momentum of 1 AO2

player A = 585 (kg m/s) 4.5.7.1

4.5.7.2

momentum of 1

player B = –500.5 (kg m/s)

(–500.5 + 585) 84.5 allow 1085.5 1

OR

(78 + 91) 169 169

= 0.5 (m/s) this answer only 1

05.3 (protective pads) increase the allow increases impact / contact 1 AO1

time taken to stop (during the / collision time 4.5.7.3

collision) do not allow slows down time

so the rate of change of allow reduces 1

momentum decreases acceleration/deceleration

allow increases the time to

reduce the momentum to zero

for 2 marks

reducing the force (on the ice allow impact for force 1

hockey player) do not allow if linked to an

incorrect explanation

Total 8

How to answer it

Momentum, Collisions and Safety Equipment

What this question tests

This question tests your understanding of the conservation of momentum in closed systems, multi-step calculation skills involving mass and velocity vectors (positive and negative directions), and the application of Newton's second law to explain how safety features like foam pads reduce impact forces by increasing collision time.

Question 05.1 (1 Mark)

Definition of Momentum Conservation

✅ Correct Answer

Total momentum before = total momentum after (or "total momentum stays the same").

💡 Key Knowledge

In a closed system (where no external forces act), the total momentum of colliding objects before the collision is equal to the total momentum after the collision.

Mark breakdown: 1 mark for stating that momentum before equals momentum after.

Question 05.2 (4 Marks)

Calculation of Velocity After Collision

📐 Step-by-Step Calculation

Calculate momentum of Player A:
78 kg × 7.5 m/s = 585 kg m/s
Calculate momentum of Player B:
91 kg × (-5.5 m/s) = -500.5 kg m/s (Notice the negative sign because Player B moves in the opposite direction).
Calculate total momentum before collision:
585 + (-500.5) = 84.5 kg m/s
Set up the equation for combined mass after collision:
Total Mass = 78 + 91 = 169 kg
Velocity = Total Momentum / Total Mass = 84.5 / 169
Final Answer:
0.5 m/s

❌ Common Calculation Traps

Ignoring signs: Forgetting to make Player B's velocity negative leads to adding the momenta instead of finding the resultant.
Incorrect mass addition: Forgetting to combine both players' masses ( 78 + 91 ) in the final division step.

Mark breakdown: 1 mark for Player A's momentum, 1 mark for Player B's momentum (with correct sign), 1 mark for correct method of combining momentum and mass, 1 mark for the final correct answer of 0.5 m/s .

Question 05.3 (3 Marks)

Explaining Safety Pads and Force Reduction

✅ Correct Answer

1. Protective pads increase the time taken to stop (during the collision).
2. Therefore, the rate of change of momentum decreases.
3. This reduces the force on the ice hockey player.

🧠 Exam Technique & Phrasing

Examiners look for a logical chain of cause and effect: Time increases ➔ Rate of change of momentum decreases ➔ Force decreases. Avoid vague statements like "it cushions the blow" without linking it to time and momentum.

Mark breakdown: 1 mark for stating time increases, 1 mark for linking this to a decreased rate of change of momentum, and 1 mark for concluding that the force on the player is reduced.

Topics

Physics · P5: Forces