Question

An observer starts to move with a velocity of $5\text{m/s}$ as shown in the figure. For what time interval the observer will be able to see his own image in the mirror after he starts moving.

• A. $1\text{s}$
• B. $\frac{4}{3}\text{s}$
• C. $\frac{10}{3}\text{s}$
• D. $\frac{5}{3}\text{s}$

Answer 1

The correct option is D $\frac{5}{3}\text{s}$

From the figure it is clear that, once the moving object crosses the line $AB$ he will no longer be able see his own image in the mirror.

Therefore, time interval for which observer will be able to see his own image in the mirror $=$ time taken by object to move the horizontal distance $OB$
$t=\frac{OB}{v\sin {37}^{\circ }}$
$t=\frac{5}{5\times \frac{3}{5}}$
$t=\frac{5}{3}\text{s}$