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Vector Algebra question

2024 · 5 Apr · Shift 1 · Q78
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  5. /2024 · 5 Apr · Shift 1 · Q78

Vector Algebra question

2024 · 5 Apr · Shift 1 · Q78

JEE MainPhysicsVector AlgebraMCQ+4 / −1
The angle between vector Q⃗\vec{Q}Q​ and the resultant of (2Q⃗+2P⃗)(2 \vec{Q}+2 \vec{P})(2Q​+2P) and (2Q⃗−2P⃗)(2 \vec{Q}-2 \vec{P})(2Q​−2P) is :
  1. A
    tan⁡−1(P/Q)\tan ^{-1}(\mathrm{P} / \mathrm{Q})tan−1(P/Q)
  2. B
    0 ∘^\circ∘
  3. C
    tan⁡−1(2Q⃗−2P⃗)2Q⃗+2P⃗\tan ^{-1} \frac{(2 \vec{Q}-2 \vec{P})}{2 \vec{Q}+2 \vec{P}}tan−12Q​+2P(2Q​−2P)​
  4. D
    tan⁡−1(2Q/P)\tan ^{-1}(2 Q / \mathrm{P})tan−1(2Q/P)
View written solutionFree

Correct answer: B

  1. Write the two given vectors

The vectors are: A⃗=2Q⃗+2P⃗\vec{A}=2\vec{Q}+2\vec{P}A=2Q​+2P B⃗=2Q⃗−2P⃗\vec{B}=2\vec{Q}-2\vec{P}B=2Q​−2P

  1. Find their resultant

The resultant of two vectors is their sum: R⃗=A⃗+B⃗\vec{R}=\vec{A}+\vec{B}R=A+B

Substituting: R⃗=(2Q⃗+2P⃗)+(2Q⃗−2P⃗)\vec{R}=(2\vec{Q}+2\vec{P})+(2\vec{Q}-2\vec{P})R=(2Q​+2P)+(2Q​−2P)

Now simplify: R⃗=2Q⃗+2P⃗+2Q⃗−2P⃗\vec{R}=2\vec{Q}+2\vec{P}+2\vec{Q}-2\vec{P}R=2Q​+2P+2Q​−2P R⃗=4Q⃗\vec{R}=4\vec{Q}R=4Q​

  1. Compare the direction of R⃗\vec{R}R with Q⃗\vec{Q}Q​

Since R⃗=4Q⃗\vec{R}=4\vec{Q}R=4Q​ it means the resultant is a positive scalar multiple of Q⃗\vec{Q}Q​. Therefore, R⃗\vec{R}R is in the same direction as Q⃗\vec{Q}Q​.

Hence, the angle between Q⃗\vec{Q}Q​ and R⃗\vec{R}R is: 0∘0^\circ0∘

  1. Check options
  • A: tan⁡−1(P/Q)\tan^{-1}(P/Q)tan−1(P/Q) — incorrect
  • B: 0∘0^\circ0∘ — correct
  • C: expression given is not the required angle — incorrect
  • D: tan⁡−1(2Q/P)\tan^{-1}(2Q/P)tan−1(2Q/P) — incorrect

Therefore, the correct option is: B\boxed{B}B​

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