Question

A cubical room is formed with 6 plane mirrors. An insect moves along a diagonal of the floor with uniform speed. The velocity of its image relative to the mirror in two adjacent walls are 20 $\sqrt{2}$ cm/s. Then the velocity of image formed by the roof is

• A. 20cm/s
• B. 40cm/s
• C. 20$\sqrt{2}$ cm/s
• D. 10$\sqrt{2}$ cm/s

Answer 1

Answer: (B)

40cm/s

We know that only the velocity component $\perp$ to a mirror surface is seen in the mirror

$\Rightarrow \frac{v}{\sqrt{2}}=20\sqrt{2}\frac{m}{s}$

$v=20\times 2=40cm/s$

Hence the velocity as seen on roof $=40cm/s.$