Question

at what distance from a concave mirror of focal length 10cm should an object 2cm long be placed in order to get an erect image 6cm tall?

Answer 1

f = -10 cm
Height of the object ho = 2 cm
Height of the image hi = 6 cm
Magnification m = hi/ho = 6/2 = 3 (erect image)
m = -v/u
3 = -v/u ⇒ v = -3u
Mirror formula: 1/v + 1/u = 1/f
1/(-3u) + 1/u = 1/(-10)
⇒ u = -20/3 = -6.7 cm