Question

A man of height 170 cm wants to see his complete image in a plane mirror (while standing). His eyes are at a height of 160 cm from the ground.

• A. minimum length of the mirror $=$ 80 cm
• B. minimum length of the mirror $=$ 85 cm
• C. bottom of the mirror should be at a height 80 cm or more
• D. bottom of the mirror should be at a height 85 cm

Answer 1

Answer: (B)

from the similar triangles RES and BEC in the above figure:

$\frac{RS}{BC}=\frac{2d}{d}$

$BC=85cm$(minimum length of the mirror)

from the similar triangles SEQ and SEO in the above figure:

$\frac{EQ}{CO}=\frac{2d}{d}$

$CO=80cm$ (bottom of the mirror should be at a height of 85cm or less)