# Homework Help: Mirror questions

1. May 30, 2005

### chase222

I have 2 questions:
What type and height of image would a rearview mirror produce of a car that was 1.3 m high and 15.0 m behind you, assuming the mirror's radius of curvature is 3.2 m?

I don't know what equation to use to solve the problem. I think it might be:
(1/object distance) + (1/image distance) = 1/f

However, w/ this equation I don't know where to plug in the height (1.3 m). Please help!

The other question is:
A mirror at an amusement park shows an upright image of any person who stands 1.3 m in front of it. If the image is three times the person's height, what is the radius of curvature?

However, I don't understand how to solve it if we don't know how big the image is. I also know that f=r/2, which I might need later on in the problem.

Thanks!

2. May 30, 2005

### Chi Meson

You noticed that f = r/2. You need this for the first question along with the knowledge that the sideview mirror on a car is a diverging mirror. THis means that the focal length must have a negative sign. You have the correct equation, just remember to use a negative focal length.

There is also the magnification equation which says (h_image / h_object) = (d-image / d_object). You might find this useful for both questions.

And only a diverging mirror (positive focal length) can create an upright AND larger image.