Convex Mirrors and Magnification

[kc262]

Homework Statement

What is the image distance for an automobile 4.5 m in front of a convex miror with a 0.15 m focal length? I found this to be 0.155 m

The question I'm having a problem with is: What is the magnification?

Homework Equations

magnification = - (image distance/object distance)

The Attempt at a Solution

I thought it would simply be,
-[0.155m/4.5m] = -0.0344. But it's not.

Some help would be much appreciated

 

[Doc Al]

What is the image distance for an automobile 4.5 m in front of a convex miror with a 0.15 m focal length? I found this to be 0.155 m

Careful with signs. For a convex mirror, what sign will the focal length have?

 

[kc262]

Careful with signs. For a convex mirror, what sign will the focal length have?

I realized that because it is a convex mirror, the focal length would be negative. However the marking program marked my answer right. I was confused by this And because of this discrepancy, I am unsure of how to find the magnification.

 

[Redbelly98]

Is the image real or virtual? (And therefore, is the image distance positive or negative?)

 

[Doc Al]

I realized that because it is a convex mirror, the focal length would be negative.

Then how did you get an image distance of +0.155 m ? (See Redbelly98's comment.)

However the marking program marked my answer right. I was confused by this

Now I'm confused. Your first post seemed to indicate that you knew your answer was wrong.

And because of this discrepancy, I am unsure of how to find the magnification.

You find it just as you stated in your first post:

magnification = - (image distance/object distance)

But you need the correct image distance (correct in both magnitude and sign), of course.

 

[kc262]

ok.. i got it. Turns out there was an error/glitch with the marking program. I got the answer in the end. Thanks for everyone's help!