A concave mirror of focal length 10 cm is placed at a distance of 35 cm from a wall. The object can be placed at a distance of ____cm from the wall, so that its image formed by the mirror falls on the wall.

A concave mirror of focal length

10 cm

is placed at a distance of

35 cm

from a wall. The object can be placed at a distance of

21 cm

so that its image formed by the mirror falls on the wall.
Here,
Focal length

(f) = - 10 cm

Image distance

(v) = 35 cm

Applying mirror formula,

\frac{1}{v} + \frac{1}{u} = \frac{1}{f}

Where

v

is the distance of the image from the mirror,

u

is the distance of the object from the mirror, and

f

is the focal length of the mirror.
Applying mirror formula,

\frac{1}{v} + \frac{1}{u} = \frac{1}{f}

\frac{1}{- 35} + \frac{1}{u} = \frac{1}{- 10}

u = - 14 cm

The distance of the object from the wall will be

- (35 - x)

\Rightarrow 35 - x = 14

\Rightarrow x = 21 cm .

A concave mirror of focal length $10 cm$ is placed at a distance of $35 cm$ from a wall. The object can be placed at a distance of ____ $cm$ from the wall, so that its image formed by the mirror falls on the wall.