Question

Rohit placed a pencil perpendicular to principal Axes in front of a converging mirror of focal length 30 cm the image formed is twice the size of the pencil calculate distance of the object from the mirror

Answer 1

Magnigfication = hi / ho = -v / u
We can assume it to be virtual because in a concave mirror, it is enlarged only when it is virtual. Otherwise, if you refer to the ray diagrams, they are all diminished.

The remaining procedure is correct, wherein we get -v /u = 2

So, if v = - 2u.

Using the mirror equation, 

1 / v + 1 / u = 1 /f

= -1 / 2u + 1 / u = 1 / -30

u = - 15 cms. which is between the focal length and the mirror. This proves that the image will be virtual and enlarged.

Answer 2

m= -v/u

-v/u = 2

v= -2u

mirror formula

1/v + 1/u = 1/f

1/-2u + 1/u = -1/30    (substitute v= -2u)

u= -15 cm