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JEE Main 2020 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 2 September 2020, Shift 1, Physics Q6

Question 6 of 75 in this shift, Physics question 6 of 25.

The mass density of a spherical galaxy varies as

\frac{K}{r}

over a large distance 'r' from its centre. In that region, a small star is in a circular orbit of radius

R

. Then the period of revolution,

T

depends on

R

as :

(1) $T^{2}\propto R^{3}$
(2) $T^{2}\propto R$ Official answer
(3) $T\propto R$
(4) $T^{2}\propto\frac{1}{R^{3}}$

Official answer

Option 2

NTA final key (Sep 2020).

Chapter: Gravitation
Topic: Orbital Mechanics
Idea tested: Orbital Time Period

Same idea in other shifts

Asked 2× in all

2 Apr 2026, Shift 1 · Q30A planet ( $P_1$ ) is moving around the star of mass $2M$ in the orbit of radius $R$ . Another planet ( $P_2$ ) is moving around another star…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. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.