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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceSingle correctMediumCalculation

JEE Main 31 August 2021, Shift 1, Physics Q16

Question 16 of 90 in this shift, Physics question 16 of 30, Section A.

A uniform heavy rod of weight 10 kg ms−2^{-2}, cross-sectional area 100 cm2^2 and length 20 cm is hanging from a fixed support. Young modulus of the material of the rod is 2×10112\times10^{11} Nm−2^{-2}. Neglecting the lateral contraction, find the elongation of rod due to its own weight :
  1. (1)2×10−92\times10^{-9} m
  2. (2)5×10−105\times10^{-10} mOfficial answer
  3. (3)5×10−85\times10^{-8} m
  4. (4)4×10−84\times10^{-8} m

Official answer

Option 2

NTA final key.

Chapter
Mechanical Properties of Solids
Topic
Elasticity
Idea tested
Elongation Due to Self-Weight

Same idea in other shifts

Asked 4× in all
  1. 2 Apr 2026, Shift 1 · Q49A uniform wire of length ll of weight ww is suspended from the roof with a weight of WW at the other end. The stress in the wire at…MediumNumerical value
  2. 26 Jul 2022, Shift 2 · Q55A uniform heavy rod of mass 20 kg, cross sectional area 0.4 m20.4\ m^2 and length 20 m is hanging from a fixed support. Neglecting the lateral…MediumNumerical value
  3. 26 Jun 2022, Shift 1 · Q54The elongation of a wire on the surface of the earth is 10−410^{-4} m. The same wire of same dimensions is elongated by 6×10−56\times10^{-5} m…EasyNumerical value

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. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.