3-2.Motion in Plane
normal

The vector sum of two forces is perpendicular to their vector differences. In that case, the forces

A

cannot be predicted

B

are equal to each other

C

are equal to each other in magnitude

D

are not equal to each other in magnitude

Solution

$\overrightarrow{\mathrm{P}}=$ vector $\mathrm{sum}=\overrightarrow{\mathrm{A}}+\overrightarrow{\mathrm{B}}$

$\overrightarrow{\mathrm{Q}}=$ vector differences $=\overrightarrow{\mathrm{A}}-\overrightarrow{\mathrm{B}}$

Since $\overrightarrow{\mathrm{P}}$ and $\overrightarrow{\mathrm{Q}}$ are perpendicular

$\therefore \overrightarrow{\mathrm{P}} \cdot \overrightarrow{\mathrm{Q}}=0$

$\Rightarrow(\overrightarrow{\mathrm{A}}+\overrightarrow{\mathrm{B}}) \cdot(\overrightarrow{\mathrm{A}}-\overrightarrow{\mathrm{B}})=0 \Rightarrow \mathrm{A}^{2}=\mathrm{B}^{2}$

$\Rightarrow|\mathrm{A}|=|\mathrm{B}|$

Standard 11
Physics

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