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Rotational Motion question

2021 · 27 Jul · Shift 1 · Q51
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  5. /2021 · 27 Jul · Shift 1 · Q51

Rotational Motion question

2021 · 27 Jul · Shift 1 · Q51

JEE MainPhysicsRotational MotionMCQ+4 / −1
List-I List-II
(a) MI of the rod (length L, Mass M, about an axis ⊥\bot⊥ to the rod passing through the midpoint) (i) 8ML2/38M{L^2}/38ML2/3
(b) MI of the rod (length L, Mass 2M, about an axis ⊥\bot⊥ to the rod passing through one of its end) (ii) ML2/3M{L^2}/3ML2/3
(c) MI of the rod (length 2L, Mass M, about an axis ⊥\bot⊥ to the rod passing through its midpoint) (iii) ML2/12M{L^2}/12ML2/12
(d) MI of the rod (Length 2L, Mass 2M, about an axis ⊥\bot⊥ to the rod passing through one of its end) (iv) 2ML2/32M{L^2}/32ML2/3


Choose the correct answer from the options given below:
  1. A
    (a)-(ii), (b)-(iii), (c)-(i), (d)-(iv)
  2. B
    (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
  3. C
    (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
  4. D
    (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
View written solutionFree

Correct answer: C

  1. Use standard formulas for a uniform rod

For a rod of length lll and mass mmm:

  • About an axis perpendicular to the rod through its midpoint: Icenter=112ml2I_{\text{center}}=\frac{1}{12}ml^2Icenter​=121​ml2

  • About an axis perpendicular to the rod through one end: Iend=13ml2I_{\text{end}}=\frac{1}{3}ml^2Iend​=31​ml2


  1. Evaluate each item in List-I

(a) Rod of length LLL, mass MMM, axis through midpoint

Using I=112ML2I=\frac{1}{12}ML^2I=121​ML2 So, (a)→ML212(a) \to \frac{ML^2}{12}(a)→12ML2​ This matches (iii).


(b) Rod of length LLL, mass 2M2M2M, axis through one end

Using I=13(2M)L2=2ML23I=\frac{1}{3}(2M)L^2=\frac{2ML^2}{3}I=31​(2M)L2=32ML2​ So, (b)→2ML23(b) \to \frac{2ML^2}{3}(b)→32ML2​ This matches (iv).


(c) Rod of length 2L2L2L, mass MMM, axis through midpoint

Using I=112M(2L)2=112M⋅4L2=ML23I=\frac{1}{12}M(2L)^2=\frac{1}{12}M\cdot 4L^2=\frac{ML^2}{3}I=121​M(2L)2=121​M⋅4L2=3ML2​ So, (c)→ML23(c) \to \frac{ML^2}{3}(c)→3ML2​ This matches (ii).


(d) Rod of length 2L2L2L, mass 2M2M2M, axis through one end

Using I=13(2M)(2L)2=13⋅2M⋅4L2=8ML23I=\frac{1}{3}(2M)(2L)^2=\frac{1}{3}\cdot 2M \cdot 4L^2=\frac{8ML^2}{3}I=31​(2M)(2L)2=31​⋅2M⋅4L2=38ML2​ So, (d)→8ML23(d) \to \frac{8ML^2}{3}(d)→38ML2​ This matches (i).


  1. Final matching

Thus,

  • (a)→(iii)(a) \to (iii)(a)→(iii)
  • (b)→(iv)(b) \to (iv)(b)→(iv)
  • (c)→(ii)(c) \to (ii)(c)→(ii)
  • (d)→(i)(d) \to (i)(d)→(i)

This corresponds to Option C.


  1. Comparison with stored answer

Stored correct answer = C

My derived answer = C

So, the derived answer agrees with the stored answer.

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