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Vector Algebra question

2022 · 26 Jul · Shift 2 · Q58
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  5. /2022 · 26 Jul · Shift 2 · Q58

Vector Algebra question

2022 · 26 Jul · Shift 2 · Q58

JEE MainPhysicsVector AlgebraNumerical+4 / −1
If A⃗=(2i^+3j^−k^) m\vec{A}=(2 \hat{i}+3 \hat{j}-\hat{k})\, \mathrm{m}A=(2i^+3j^​−k^)m and B⃗=(i^+2j^+2k^) m\vec{B}=(\hat{i}+2 \hat{j}+2 \hat{k}) \,\mathrm{m}B=(i^+2j^​+2k^)m. The magnitude of component of vector A⃗\vec{A}A along vector B⃗\vec{B}B will be ‾\underline{\hspace{2cm}}​m\mathrm{m}m.
Numerical answer
View written solutionFree

Correct answer: 2

  1. Given vectors

A⃗=2i^+3j^−k^\vec A = 2\hat i + 3\hat j - \hat kA=2i^+3j^​−k^ B⃗=i^+2j^+2k^\vec B = \hat i + 2\hat j + 2\hat kB=i^+2j^​+2k^

We need the magnitude of the component of A⃗\vec AA along B⃗\vec BB.

  1. Formula for scalar component (projection) of A⃗\vec AA along B⃗\vec BB

Component of A⃗ along B⃗=A⃗⋅B⃗∣B⃗∣\text{Component of } \vec A \text{ along } \vec B = \frac{\vec A \cdot \vec B}{|\vec B|}Component of A along B=∣B∣A⋅B​

Since the question asks for the magnitude, we take the absolute value if needed.

  1. Find the dot product

A⃗⋅B⃗=(2)(1)+(3)(2)+(−1)(2)\vec A \cdot \vec B = (2)(1) + (3)(2) + (-1)(2)A⋅B=(2)(1)+(3)(2)+(−1)(2)

=2+6−2=6= 2 + 6 - 2 = 6=2+6−2=6

  1. Find the magnitude of B⃗\vec BB

∣B⃗∣=12+22+22=1+4+4=9=3|\vec B| = \sqrt{1^2 + 2^2 + 2^2} = \sqrt{1+4+4} = \sqrt{9} = 3∣B∣=12+22+22​=1+4+4​=9​=3

  1. Compute the component

A⃗⋅B⃗∣B⃗∣=63=2\frac{\vec A \cdot \vec B}{|\vec B|} = \frac{6}{3} = 2∣B∣A⋅B​=36​=2

So, the magnitude of the component of A⃗\vec AA along B⃗\vec BB is

2 m\boxed{2\ \text{m}}2 m​

  1. Comparison with stored answer

Stored correct answer: 222

Our derived answer is also 222, so it agrees.

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