Question

How far should an object be from the pole of concave mirror of focal length 20 cm to form a real image whose size is 1/5 th of the size of the object

Answer 1

f = -20m = -v/ u-1 / 5 = - v / uv = u / 5 .......... 11 / f = 1 / v +1 / u1 / -20 = 5 / u + 1 / u ( from 1 )-1 / 20 = 6 / uu = 6 *(-20)u = -120
object distance =120