Question

An Object is placed at a certain distance on the principle axis of a concave mirror. The image is formed at distance of 30 cm from the mirror. Find the object distance if radius of curvature is 15cm

Answer 1

given image distance(v) :-30cm
          radius of curvature(R):-15cm
to find the distance of object:-u 

as we know the formula of mirror:- 1/v + 1/u =1/f
                          to find the focal length(f)=R/2
                                                              (f)= -15/2cm

1/30 + 1/u =1/-15/2
1/u= -2/15 + (-1/30)
1/u=-2/15 - 1/30
1/u= -5/30
1/u= -1/6
   u= -6cm

hope it is clear.....