CBSE Past Year MCQ Quiz

Assertion \((A)\) : The vectors \(\overrightarrow{\mathrm{a}}\) and \((-2 \overrightarrow{\mathrm{a}})\), where \(\overrightarrow{\mathrm{a}} \neq \overrightarrow{0}\) are collinear vectors.
\(\operatorname{Reason}(R): \quad \overrightarrow{\mathrm{a}} \cdot(-2 \overrightarrow{\mathrm{a}})=0\).

If projection of \(\vec{a}=\alpha \hat{i}+\hat{j}+4 \hat{k}\) on \(\vec{b}=2 \hat{i}+6 \hat{j}+3 \hat{k}\) is 4 units, then \(\alpha\) is