Solving Lens Image Problem: Where is Image Formed?

[jmb07]

An object 1.95 cm high is placed 11.2 cm in front of a convex mirror with a radius of curvature of 9.8 cm. Where is the image formed??

So i know Di= (Doxf)/(Do+f)...(11.2 x 9.8)/ (11.2 + 9.8) = 5.23 cm

However, the correct answer is 3.41 cm

What am i doing wrong here? I know that the 9.8 may not be the focal length but how do i relate the height to the focal length??

 

[rl.bhat]

Focal length of the convex mirror = R/2 = 9.8/2 = 4.9 cm.

 

[jmb07]

do i even need to use the height of the object??...if so how?

 

[jmb07]

nevermind i got it! thanks!