Question

A boy of height 1.5 m with his eye level at 1.4 m stands before a plane mirror of length 0.75 m fixed on the wall. The height of the lower edge of the mirror above the floor is 0.8 m. Then :

• A. the boy can't see his hair
• B. the boy can't see his feet
• C. the boy will see his full image
• D. the boy can see neither his hair nor his feet

Answer 1

Answer: (B)

$\frac{d+x}{0.8}=\frac{2d+x}{1.4}$ (By similar triangles)

$⟹1.4d+1.4x=1.6d+0.8x$

$⟹x=\frac{d}{3}$

By similar triangles,

$\frac{x}{h}=\frac{x+d}{0.8}$

$⟹\frac{d}{3h}=\frac{4d}{2.4}$

$⟹h=\frac{2.4}{3\times 4}=0.2m$

Hence the person cannot see his feet i.e. the bottom 0.2 meter of his body.