MCQEasyJEE 2023Dimensions & Dimensional Analysis

JEE Physics 2023 Question with Solution

Match List I with List II:

A matching table with List I containing A. Spring constant, B. Angular speed, C. Angular momentum, D. Moment of Inertia, and List II containing I. $$T^{-1}$$, II. $$MT^{-2}$$, III. $$ML^2$$, IV. $$ML^2T^{-1}$$.

Choose the correct answer from the options given below:

  • A

    A-II, B-I, C-IV, D-III

  • B

    A-IV, B-I, C-III, D-II

  • C

    A-II, B-III, C-I, D-IV

  • D

    A-I, B-III, C-II, D-IV

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: Match physical quantities in List I with their dimensions in List II.

Find: The correct matching.

Dimensions:

Angular speedT1Spring constantMT2Moment of inertiaML2Angular momentumML2T1\begin{aligned} \text{Angular speed} &\to T^{-1} \\ \text{Spring constant} &\to MT^{-2} \\ \text{Moment of inertia} &\to ML^2 \\ \text{Angular momentum} &\to ML^2T^{-1} \end{aligned}

Therefore,

AII,BI,CIV,DIIIA \to II, \quad B \to I, \quad C \to IV, \quad D \to III

So the correct option should be A.

The solution concludes with D, but its working is unrelated to this question. Using the dimensional analysis shown by the question itself, the defensible answer is A.

Common mistakes

  • Confusing angular speed with angular momentum. Angular speed has dimension T1T^{-1}, whereas angular momentum has dimension ML2T1ML^2T^{-1}. Match the quantity with its defining formula first.

  • Assigning moment of inertia the dimension of force-related quantities. Moment of inertia is based on mr2mr^2, so its dimension is ML2ML^2, not MT2MT^{-2}. Use the mass-distance definition.

  • Using the incorrect dimension for spring constant. From F=kxF = kx, we get k=F/xk = F/x, so dimension is MT2MT^{-2}. Do not forget that dividing force by length removes one power of LL.

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