A reflecting, spherical Christmas tree ornament has a diameter of 7.0 cm. A child looks at the ornament from a distance of 16 cm.
Where is the image located?
This is a convex mirror. The focal point is MIDWAY betwen the center of curvature and the lens surface and is NEGATIVE
So for this mirror f = -1.75 (1/2 of the RADIUS) It will produce a virtual image on the same side as the focal point (opposite the side of the OBJECT ....the child's face) so the distance result will be negative thusly:
1/f = 1/do + 1/di do = distance to the object = 16cm f = - 1.75 solve for di
-1/1.75 = 1/16 + 1/di
-1/1.75 - 1/16 = 1/di
di = - 1.58 cm