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Laws of Motion question

2022 · Q162
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  5. /2022 · Q162

Laws of Motion question

2022 · Q162

NEETPhysicsLaws of MotionMCQ+4 / −1

If F→=2i^+j^−k^\overrightarrow F = 2\widehat i + \widehat j - \widehat kF=2i+j​−k and r→=3i^+2j^−2k^\overrightarrow r = 3\widehat i + 2\widehat j - 2\widehat kr=3i+2j​−2k, then the scalar and vector products of F→\overrightarrow FF and r→\overrightarrow rr have the magnitudes respectively as

  1. A
    10, 2
  2. B
    5, 3\sqrt 33​
  3. C
    4, 5\sqrt 55​
  4. D
    10, 2\sqrt 22​
View written solutionFree

Correct answer: D

Given, $$\overrightarrow F = 2\widehat i + \widehat j - \widehat k$$ and $$\overrightarrow r = 3\widehat i + 2\widehat j - 2\widehat k$$

$$\overrightarrow F \,.\,\overrightarrow r = 2(3) + 2(1) + ( - 2)( - 1)$$

$ = 6 + 2 + 2 = 10$

$$\overrightarrow F \times \overrightarrow r = \left| {\begin{matrix} {\widehat i} & {\widehat j} & {\widehat k} \\ 2 & 1 & { - 1} \\ 3 & 2 & { - 2} \\

\end{matrix} } \right|$$

$$ = \widehat i( - 2 + 2) - \widehat j( - 4 + 3) + \widehat k(4 - 3)$$

$$ \Rightarrow \overrightarrow F \times \overrightarrow r = \widehat j + \widehat k$$

$$|\overrightarrow F \times \overrightarrow r | = \sqrt {{1^2} + {1^2}} = \sqrt 2 $$

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