Physics repost
posted by Jon on .
1)A 5.0 cm real object is placed at a distance of 5.0 cm from a concave mirror of focal length 10 cm. Find the size of the image.
di= 10
magnification = di/do
magnification = 10/5.0
magnification = 2
image size = (object size)*(magnification)
image size = (5.0)*(2)
image size = 10 cm (all of that is from the equation drwls gave me)
2)A rod of length 5.0 cm lies along the axis of a concave mirror of radius of curvature 20 cm. The end of the rod closer to the mirror is 15 cm from the mirror. Find the length of the image of the rod.
20/2
10 cm

Yes on 1, and a quick ray diagram ought to confirm it.
On number 2, find the di for each end of the rod, then the difference is the length. I didn't compute it, but your work indicates you handled it as an image perpendicular to the principal axis, which it is not. I will be happy to critique your work on this. 
2)f=10
di=(10)(5)/510
di=10
di=(10)(15)/1510
di=30
you said the difference is the length, so it would be 3010 which would be 30+10=40? or 3010=20? I got confused on that part 
Not checking your math, if it is 10 and 30, the distance between those points is 40cm.