Question

The vector $\stackrel{-}{A}=0.4\hat{i}+0.8\hat{j}+c\hat{k}$ represents a unit vector, then $c$ must be:

• A. $-0.2$
• B. $\sqrt{0.2}$
• C. $\sqrt{0.8}$
• D. $0$

Answer 1

The correct option is B $\sqrt{0.2}$

Given:

$\left|A\right|=\sqrt{{0.4}^2+{0.8}^2+c^2}=1$
$0.16+0.64+c^2=1$
$c^2=1-0.80=0.2$
$c=\sqrt{0.2}$