Kinematics Question 274
Question: The vector $ \overrightarrow{P}=a\hat{i}+a\hat{j}+3\hat{k} $ and $ \overrightarrow{Q}=a\hat{i}-2\hat{j}-\hat{k} $ are perpendicular to each other. The positive value of a is [AFMC 2000; AIIMS 2002]
Options:
A) 3
B) 4
C) 9
D) 13
Correct Answer: A $ \bar{P}.\bar{Q}=0 $ $ a^{2}-2a-3=0 $
therefore $ a=3 $
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