Answer to Question #93146 in Optics for Sridhar

Question

A girl of height 150 cm with her eye level at 140 cm stands in front of a plane mirror of height 75 cm fixed to a wall. The lower edge of the mirror is at a height of 85 cm above her feet level. The height of her image the girl can see in the mirror is

Answer 1

Find the image DB. This

$DB=CB+DC$

Find CB from the likeness of triangles AB'C' and ABC

$\frac{CB}{C'B'}=\frac{1}{2}$

Then

$C'B'=75-(75+85)+140=55 (cm)$

$DC=150-140=10(cm)$

So

$DB=110+10=120 (cm)$

Answer: The height of her image the girl can see in the mirror is 120 cm