Question

 An object is placed at the zero-mark of a meterstick while its image appears at the +15 cm mark using 

a convex mirror with a focal length of magnitude |𝑓𝑓| = 10 cm. Where is the mirror placed?

Answer 1

f=10cm

v=15

Mirror equation

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

$\frac{1}{u}=\frac{1}{f}-\frac{1}v$

$\frac{1}{u}=\frac{1}{10}-\frac{1}{15}$

$u=\frac{15\times10}{15-10}=30cm$