Question

A man is $180cm$ tall and his eyes are $10cm$ below the top of his head. In order to see his entire height right from toe to head, he uses a plane mirror kept at a distance of $1m$ from him. The minimum length of the plane mirror required is :

• A. $180cm$
• B. $90cm$
• C. $85cm$
• D. $170cm$

Answer 1

The correct option is B $90cm$

Minimum length of plane mirror required in such cases doesn't depend on distance of object from the mirror and is always equal to half of height of object.

$\therefore$ length of mirror$=\frac{180}{2}=90cm$