JEE Main 2019PhysicsMathematics in PhysicsEasyMCQ

JEE Main 2019Mathematics in Physics Question with Solution

JEE Main 2019 (10 Jan Shift 2)

Question

Two forces P and Q, of magnitude 2F and 3F, respectively, are at an angle θ with each other. If the force Q is doubled, then their resultant also gets doubled. Then, the angle θ is:

Choose an option

Show full solutionCorrect option: A
Correct answer
A120°

Step-by-step explanation

P=2F,Q=3F

R=P2+Q2+2PQcosθ

=4F2+9F2+12F2cosθ=F13+12cosθ

If Q is doubled

2R=4F2+36F2+24F2cosθ=F40+24cosθ

413+12cosθ=40+24cosθ

12=-24cosθ

cosθ=-12

θ=120°

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About this question

This is a previous-year question from JEE Main 2019, covering the Mathematics in Physics chapter of Physics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.