AQA A-Level Mathematics Paper 2, June 2025: Question 11

1 mark · Easy difficulty · Short Answer

Find the coefficient of friction given a normal reaction force of 125 N and a frictional force of 40 N.

Practise this question

Question

Question 11: An object is pulled along a horizontal surface. The normal reaction between the surface and the object is 125 newtons. The object experiences a constant frictional force of 40 newtons. Find the value of the coefficient of friction. Circle your answer. Four numerical options are provided: 0.245, 0.32, 0.5, and 3.125.
Question text

11 An object is pulled along a horizontal surface. The normal reaction between the

surface and the object is 125 newtons.

The object experiences a constant frictional force of 40 newtons.

Find the value of the coefficient of friction.

Circle your answer.

[1 mark]

0.245 0.32 0.5 3.125

Mark scheme

Show the mark scheme Mark scheme table for Question 11 showing 1 mark total. Marking instructions state 'Circles the second answer' with assessment objective AO 3.3, mark B1, and typical solution '0.32'.

Q Marking instructions AO Marks Typical solution

11 Circles the second answer 3.3 B1 0.32

Question 11 Total 1

How to answer it

Calculating the Coefficient of Friction on a Horizontal Surface

📌 What this question tests

This multiple-choice question assesses your fundamental understanding of the friction model in mechanics (AO3.3):

  • Recalling and applying the standard friction law for a moving object: F = μR .
  • Correctly identifying the normal reaction force ( R ) and frictional force ( F ).
  • Rearranging the formula to calculate the dimensionless coefficient of friction ( μ ).

Question 11 Walkthrough

1 Mark • Multiple Choice (AO 3.3)

✅ Correct Answer

0.32

The second option must be circled.

Mark Scheme Breakdown:
• B1: Circles 0.32 (unambiguous selection).

💡 Key Knowledge

  • Limiting / Dynamic Friction: When an object is moving (in motion), friction reaches its maximum possible value and is given by F = μR .
  • F = Frictional force parallel to the surface (in N).
  • R = Normal reaction force perpendicular to the surface (in N).
  • μ = Coefficient of friction (a dimensionless ratio, typically between 0 and 1).

📐 Step-by-Step Calculation

  1. Identify the given values:
    Normal reaction force, R = 125 N
    Frictional force, F = 40 N
  2. State the relationship:
    Since the object is pulled along the surface and experiences dynamic friction:
    F = μR
  3. Rearrange for μ:
    μ = F / R
  4. Substitute the numbers:
    μ = 40 / 125 = 8 / 25 = 0.32

❌ Common Errors & Distractor Traps

  • Inverting the fraction (3.125): Dividing R / F = 125 / 40 = 3.125 . Coefficients of friction in mechanics problems are rarely greater than 1. An answer over 3 should immediately trigger a sanity check!
  • Unnecessary multiplication by g (0.245 or similar): Mistaking the normal reaction force (125 N) for a mass in kg and multiplying/dividing by 9.8. The value was already given in Newtons!
  • Random guessing (0.5): Picking a "standard" textbook value without performing the simple one-step division.

🧠 Exam Technique & Examiner Insights

  • No working needed for B marks: While working helps prevent arithmetic slips, only the final circled choice is marked. Make sure your selection is completely unambiguous.
  • Correcting a mistake: If you change your mind, cross through the incorrect choice clearly and circle the new one. If two choices appear circled, examiners cannot award the mark.
  • Units Check: Remember that μ has no units because it is Newtons divided by Newtons ( N / N ).

Topics

Mechanics · R: Forces and Newton’s laws

Question and mark scheme from the AQA A-Level Mathematics examination, Paper 2, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.