Question

When a plane mirror $AB$ is placed horizontally on level ground, with $B$ at a distance of $60m$ from the foot of a tower, the top of the tower and its image in the mirror subtends, an angle of ${90}^{\circ }$ at $B$. The height of the tower is

• A. $30m$
• B. $60m$
• C. $90m$
• D. $120m$

Answer 1

The correct option is B $60m$


As the top of the tower and its image in the mirror subtends, an angle of ${90}^{\circ }$ at $B$.
As size of image is equal to size of object, tower exerts ${45}^{\circ }$ at $B$.
So,
$\tan {45}^{\circ }=\frac{y}{60}\Rightarrow y=60m$