Question

If the velocities of two objects A and B are $7\hat{i}$ and $24\hat{k}$, then the magnitude of relative speed of A with respect to B will be

• A. 31
• B. 25
• C. 17
• D. 15

Answer 1

The correct option is B 25

$\overrightarrow{V_{rel}}=\overrightarrow{V_{AB}}=\overrightarrow{V_A}-\overrightarrow{V_B}$

$=7\hat{i}-24\hat{k}$
Speed $=|\overrightarrow{V_{rel}}|=|\overrightarrow{V_{\frac{A}{B}}}|=\sqrt{{24}^2+7^2}=25m/s$