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3-1.Vectors
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Figure shows three vectors $\vec{a}, \vec{b}$ and $\vec{c}$, where $R$ is the midpoint of $PQ$ . Then which of the following relations is correct?
A$\mathop {\,a}\limits^ \to \, + \mathop {\rm{b}}\limits^ \to \, = \,\,2\mathop {\,c}\limits^ \to $
B$\mathop {\,a}\limits^ \to \, + \mathop {\rm{b}}\limits^ \to \, = \,\,\mathop {\,c}\limits^ \to $
C$\mathop {\,a}\limits^ \to \, - \mathop {\rm{b}}\limits^ \to \, = \,\,2\mathop {\,c}\limits^ \to $
D$\mathop {\,a}\limits^ \to \, - \mathop {\rm{b}}\limits^ \to \, = \,\,\mathop {\,c}\limits^ \to $
Solution
Step 1: Applying triangle law of vector addition From triangle law of vector addition,
In $\triangle OPR$
$\vec{a}=\vec{c}+\overrightarrow{R P}$
and $\operatorname{In} \triangle ORQ$
$\overrightarrow{ b }=\overrightarrow{ c }+\overrightarrow{ RQ }$
Step $2:$ Equation solving
Adding $eq ^{ n }(1)$ and (2)
$\vec{a}+\vec{b}=2 \vec{c}+\overrightarrow{R P}+\overrightarrow{R Q}$
Since $R$ is midpoint of $PQ$, therefore $\overrightarrow{ RP }=-\overrightarrow{ RQ }$ $\Rightarrow \vec{a}+\vec{b}=2 \vec{c}+\overrightarrow{R P}-\overrightarrow{R P}$
$\Rightarrow \vec{a}+\vec{b}=2 \vec{c}$
In $\triangle OPR$
$\vec{a}=\vec{c}+\overrightarrow{R P}$
and $\operatorname{In} \triangle ORQ$
$\overrightarrow{ b }=\overrightarrow{ c }+\overrightarrow{ RQ }$
Step $2:$ Equation solving
Adding $eq ^{ n }(1)$ and (2)
$\vec{a}+\vec{b}=2 \vec{c}+\overrightarrow{R P}+\overrightarrow{R Q}$
Since $R$ is midpoint of $PQ$, therefore $\overrightarrow{ RP }=-\overrightarrow{ RQ }$ $\Rightarrow \vec{a}+\vec{b}=2 \vec{c}+\overrightarrow{R P}-\overrightarrow{R P}$
$\Rightarrow \vec{a}+\vec{b}=2 \vec{c}$
Standard 11
Physics