Quick physics question about optics?

Yes you can. r = 2f. The focal length for a spherical mirror is the diameter of the sphere divided by 4. So f = 2.0 cm presumably convex, so use f = negative 2cm. Since M = - image distance/object distance 0.5 = - dI/d0 so dI = - 0.5 do. Plug that into mirror equation to find do. dI = -1 and do = 2 cm.