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Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctEasyConceptual

JEE Main 3 September 2020, Shift 1, Physics Q8

Question 8 of 75 in this shift, Physics question 8 of 25.

Consider a gas of triatomic molecules. The molecules are assumed to be triangular and made of massless rigid rods whose vertices are occupied by atoms. The internal energy of a mole of the gas at temperature T is :

The figure, in words

A triangle drawn with a small open circle at each of its three vertices, joined by straight line segments (printed above the question text); no labels.
  1. (1)3RTOfficial answer
  2. (2)52\frac{5}{2}RT
  3. (3)92\frac{9}{2}RT
  4. (4)32\frac{3}{2}RT

Official answer

Option 1

NTA final key (Sep 2020).

Chapter
Kinetic Theory
Topic
Kinetic Theory of Gases
Idea tested
Linear vs Non-Linear Polyatomic DOF

Same topic in other shifts

All Kinetic Theory of Gases questions
  1. 4 Apr 2026, Shift 2 · Q33Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A: If the average kinetic…EasyAssertion–reason
  2. 5 Apr 2026, Shift 1 · Q32Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Statement I: Change in internal…MediumTwo statements
  3. 2 Apr 2025, Shift 1 · Q48γA\gamma_A is the specific heat ratio of monoatomic gas A having 3 translational degrees of freedom. γB\gamma_B is the specific heat ratio…MediumNumerical value
  4. 2 Apr 2025, Shift 2 · Q50The internal energy of air in 4 m×4 m×3 m4\ \mathrm{m}\times4\ \mathrm{m}\times3\ \mathrm{m} sized room at 1 atmospheric pressure will be…EasyNumerical value
  5. 7 Apr 2025, Shift 1 · Q33Match the LIST-I with LIST-I LIST-I | LIST-II A. Triatomic rigid gas | I. CpCv=53\frac{C_p}{C_v} = \frac{5}{3} B. Diatomic non-rigid gas | II.…MediumMatch the list
  6. 7 Apr 2025, Shift 2 · Q33The helium and argon are put in the flask at the same room temperature (300 K). The ratio of average kinetic energies (per molecule) of…EasySingle correct

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.