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Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctEasyCalculation

JEE Main 9 January 2020, Shift 2, Physics Q5

Question 5 of 75 in this shift, Physics question 5 of 25, Section A.

A rod of length LL has non-uniform linear mass density given by ρ(x)=a+b(xL)2\rho(x) = a + b\left(\frac{x}{L}\right)^2, where aa and bb are constants and 0≤x≤L0 \le x \le L. The value of xx for the centre of mass of the rod is at :
  1. (1)34(2a+b3a+b)L\frac{3}{4}\left(\frac{2a+b}{3a+b}\right)LOfficial answer
  2. (2)32(2a+b3a+b)L\frac{3}{2}\left(\frac{2a+b}{3a+b}\right)L
  3. (3)43(a+b2a+3b)L\frac{4}{3}\left(\frac{a+b}{2a+3b}\right)L
  4. (4)32(a+b2a+b)L\frac{3}{2}\left(\frac{a+b}{2a+b}\right)L

Official answer

Option 1

NTA final key (Jan 2020).

Same idea in other shifts

Asked 2× in all
  1. 28 Jul 2022, Shift 2 · Q22The distance of centre of mass from end A of a one dimensional rod (AB) having mass density ρ=ρ0(1−x2L2)\rho=\rho_0\left(1-\frac{x^2}{L^2}\right)…MediumNumerical 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.