A concave mirror of focal length 15 cm forms an image having twice the linear dimensions of the object. The position of the object when the image is virtual will be
f = -15 cm, m = + 2 (Positive because image is virtual)
∵ m = - vu⇒ v = - 2u. By using mirror formula
1−15=1(−2u)+1u⇒u=−7.5 cm