Discover the Focal Length of a Convex Mirror Using Object and Image Distance

[Bk8907]

Convex mirror. PLEASE HELP!

Homework Statement

An object 30 cm tall is placed 20 cm in front of a convex mirror. If the height of the image is +10 cm, find the focal length of the mirror.

Homework Equations

The Attempt at a Solution

I know to use 1/f = -(Image distance from V) / Object distance from V. But, now they tell me how tall they are. How to solve now?

 

[andrevdh]

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