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Saturday, 31 October

JEE Main 2021 · PhysicsNumerical answerNumerical valueMediumApplication

JEE Main 17 March 2021, Shift 2, Physics Q27

Question 27 of 90 in this shift, Physics question 27 of 30, Section B.

The disc of mass M with uniform surface mass density σ\sigma is shown in the figure. The centre of mass of the quarter disc (the shaded area) is at the position x3aπ, x3aπ\frac{x}{3}\frac{a}{\pi},\ \frac{x}{3}\frac{a}{\pi} where xx is ____________. (Round off to the Nearest Integer) [a is an area as shown in the figure ]

The figure, in words

A circle (disc) with axes X (horizontal, to the right) and Y (vertical, upwards) through its centre, drawn partly as dotted lines in the lower and left parts; the upper-right quarter between the +Y and +X axes is shaded with hatching and labelled a. A line from the centre at an angle labelled theta above the X axis cuts the shaded quarter.

Official answer

4

NTA final key.

Chapter
System of Particles and Rotational Motion
Topic
Center of Mass
Idea tested
COM of Circular Sector

Same topic in other shifts

All Center of Mass questions
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  2. 6 Apr 2026, Shift 1 · Q33The position of center of mass of three masses 2 kg, 3 kg and 15 kg placed with respect to mid point (pp) of normal bisector, as shown in…EasySingle correctHas a figure
  3. 6 Apr 2026, Shift 2 · Q32Two identical bodies A and B of equal masses have initial velocities v⃗1=4i^\vec{v}_1=4\hat{i} m/s and v⃗2=4j^\vec{v}_2=4\hat{j} m/s respectively.…MediumSingle correct
  4. 7 Apr 2025, Shift 1 · Q29A rod of length 5 L is bent right angle keeping one side length as 2 L. The position of the centre of mass of the system: (Consider L = 10…EasySingle correctHas a figure
  5. 4 Apr 2024, Shift 2 · Q58In a system two particles of masses m1m_1= 3 kgkg and m2m_2 = 2 kgkg are placed at certain distance from each other. The particle of mass…EasyNumerical value
  6. 8 Apr 2024, Shift 1 · Q52A uniform thin metal plate of mass 10 kg with dimensions is shown. The ratio of xx and yy coordinates of center of mass of plate in…MediumNumerical valueHas a figure

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.