Mirror Image: Solving for Object Height & Location

[myoplex11]

Homework Statement

an image in a convex mirror is 12cm tall and 30cm from the mirror.IF the focal length is 50cm, where is the object and how tall.

Homework Equations

(1/f)=(1/do)+(1/di)
M= hi/ho =-di / do

The Attempt at a Solution

i got 7.5cm for the object height but a convex mirror always gives a reduced image?

 

[alphysicist]

Hi myoplex11,

It's difficult to follow since you did not post the actual numbers that you used.

However, I think the problem is that you either put in the incorrect image distance, or the incorrect focal length.

 

[myoplex11]

here is my work:
(1/do)=1/50 - (-1/30)
do=18.75
ho= - (18.75/-30)*12 = 7.5

 

[alphysicist]

Since this is a convex mirror, what do you know about the focal length?

 

[myoplex11]

i am not sure

 

[myoplex11]

oh yeah focul length is negative thanks.