Question

at what distance from a concave mirror of focal length 10 cm should an object 2cm long be placed in order to get an erect image of 6cm tall.

Answer 1

f=-10 cm

height of object=2cm

distance of image=-6cm

1/f=1/v+1/u

1/u=1/f-1/v

     =1/-10 - 1/(-6)

     =1/-10+1/6

     =2/30
     =1/15
1/u=1/15
u=15cm

Answer 2

It is a concave mirror so everything is negative

U =?
f =10 cm = - 10
Height of u =2cm
Image height =6cm it is positive because erect
We know m = hi/ho
Let sub in formula
M= 6/2
Cancel it we will get the magnification at +3
So it is a last case were we will get a erect image so the object will be placed BTW pole and focus