Kinematics Question 424
Question: The vector $ \vec{P}=a\hat{i}+a\hat{j}+3\hat{k} $ and $ \vec{Q}=a\hat{i}-2\hat{j}-\hat{k} $ are perpendicular to each other. The positive value of a is
Options:
A) 3
B) 4
C) 9
D) 13
Correct Answer: A [a] $ \overrightarrow{P}.\overrightarrow{Q}=0 $ $ \Rightarrow $ $ a^{2}-2a-3=0 $ $ \Rightarrow $ $ a=3 $
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