How long is the image of the meter stick?

[rayhan619]

Homework Statement

The figure shows a meter stick held lengthwise along the optical axis of a concave mirror. (Intro 1 figure) - figure attached

How long is the image of the meter stick?

Homework Equations

1/f = 1/do + 1/di

3. The Attempt at a Solution [/b

1/di = 1/f - 1/do = 1/40 -1/60
di = 120 cm

but I am not sure how to proceed after this part

any help would be appreciated

 

[Doc Al]

You found the location of the image of one end of the stick; now find the other.

 

[rayhan619]

so for the second point
1/di = 1/f - 1/do = 1/40 - 1/160
di = 53.3

so the length of the scale would be (120+53.3) = 173.3 cm

or (120-53.3) = 66.7 cm ?

 

[Doc Al]

The length of the image will be the difference in the position of each end.