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3.1 vectors — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics3.1 vectors1 Mark
MCQ
When $\vec A.\vec B = - |A||B|,$ then
  • A
    $\vec A$ and $\vec B$ are perpendicular to each other
  • B
    $\vec A$ and $\vec B$ act in the same direction
  • ✓
    $\vec A$ and $\vec B$ act in the opposite direction
  • D
    $\vec A$ and $\vec B$ can act in any direction
✓

Answer

Correct option: C.
$\vec A$ and $\vec B$ act in the opposite direction
c
(c) $\overrightarrow A .\overrightarrow B = AB\cos \theta $

In the problem $\overrightarrow A .\overrightarrow B = - AB$ i.e. $\cos \theta = - 1$

$\theta = 180^\circ $

i.e. $\overrightarrow A $ and $\overrightarrow B $ acts in the opposite direction.

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