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Laws of Motion question

2024 · 27 Jan · Shift 2 · Q63
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  5. /2024 · 27 Jan · Shift 2 · Q63

Laws of Motion question

2024 · 27 Jan · Shift 2 · Q63

JEE MainPhysicsLaws of MotionMCQ+4 / −1
Given below are two statements : Statement (I) : The limiting force of static friction depends on the area of contact and independent of materials. Statement (II) : The limiting force of kinetic friction is independent of the area of contact and depends on materials. In the light of the above statements, choose the most appropriate answer from the options given below :
  1. A
    Statement I is incorrect but Statement II is correct
  2. B
    Both Statement I and Statement II are correct
  3. C
    Both Statement I and Statement II are incorrect
  4. D
    Statement I is correct but Statement II is incorrect
View written solutionFree

Correct answer: A

  1. Recall the laws of friction

    For dry friction between two surfaces:

    • Limiting static friction is fs,max⁡=μsNf_{s,\max} = \mu_s Nfs,max​=μs​N
    • Kinetic friction is fk=μkNf_k = \mu_k Nfk​=μk​N

    where:

    • μs,μk\mu_s, \mu_kμs​,μk​ are coefficients of friction,
    • NNN is the normal reaction.
  2. Check Statement (I)

    Statement (I): The limiting force of static friction depends on the area of contact and independent of materials.

    From fs,max⁡=μsNf_{s,\max} = \mu_s Nfs,max​=μs​N we see that limiting static friction:

    • is independent of area of contact (for ideal dry surfaces),
    • depends on the nature of materials through μs\mu_sμs​.

    Hence Statement (I) is incorrect.

  3. Check Statement (II)

    Statement (II): The limiting force of kinetic friction is independent of the area of contact and depends on materials.

    Using fk=μkNf_k = \mu_k Nfk​=μk​N kinetic friction:

    • is independent of area of contact,
    • depends on materials through μk\mu_kμk​.

    Hence Statement (II) is correct.

  4. Choose the correct option

    Therefore:

    • Statement I is incorrect
    • Statement II is correct

    So the correct option is: A\boxed{\text{A}}A​

  5. Comparison with stored answer

    Stored correct answer: A

    My derived answer: A

    They match.

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