Posted by Susan on .
A convex mirror has a focal length of
18 cm. How far behind the mirror does the image of a person 3.0 m away appear? The answer must be in cm.
The equation to use woulde be:
1/f = 1/do + 1/di
do = 300 cm
f = would it be 18 cm or 18 cm???

Physics 
drwls,
Use negatve numbers for the focal length of a convex mirror. They already tell you to use 18.
1/18 = 1/300 + 1/di
1/di = .058888
di = 16.98
Negative numbers for the di mean that the image is behind the mirror. This would be typical of a mirror used as a wideangle side view mirror for a car, or for viewing aorund a corner.