An erect image `3 times` the size of the object is obtained with a concave mirror of radius of curvature `36 cm`. What is the position of the object ?

Answer

`-12cm`

Explanation

Here, `m = 3, R = -36 cm, u = ?`
`As m= - v/u, 3 = -v/u or v = -3 u`
As `(1)/(v) + 1/u = (1)/(f) =2/R, 1/(-3u) + 1/u = 2/(-36)` or `(-1+3)/(3u) = -1/18`
or `3u = -36, u = -12 cm`.