MCQ
When $\vec{A} \cdot \vec{B}=-|A||B|$, 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) $\vec{A} \cdot \vec{B}=A B \cos \theta$In the problem $\vec{A} \cdot \vec{B}=-A B$ i.e. $\cos \theta=-1 \therefore \theta=180^{\circ}$ i.e. $\vec{A}$ and $\vec{B}$ acts in the opposite direction.

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