JEE Main 2021 · PhysicsNumerical answerNumerical valueMediumMulti-step

JEE Main 25 July 2021, Shift 1, Physics Q21

Question 21 of 90 in this shift, Physics question 21 of 30, Section B.

A body of mass 2 kg moving with a speed of 4 m/s. makes an elastic collision with another body at rest and continues to move in the original direction but with one fourth of its initial speed. The speed of the two body centre of mass is

\frac{x}{10}

m/s. Then the value of

x

is __________.

Official answer

NTA final key.

Chapter: System of Particles and Rotational Motion
Topic: Center of Mass
Idea tested: COM Velocity Conservation

Same idea in other shifts

Asked 4× in all

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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.