Question

object is placed at the centre or Centre distance on the principal axis of a concave mirror the image is formed at a distance of 30 cm from the major find object distance radius of curvature is 15 CM

Answer 1

very simple
in concave mirror when an object is placed at centre then the image forms at the same position that is at centre 
therefore the object distance = image distance = centre distance = radius of curvature
hence object distance = 15cm

also the nature of the image will be 
real, inverted, same size, at centre of curvature

if it is helpful mark as brainliest

Answer 2

F=r/2
=15/2
Now from mirror formula
1/f=1/v+1/u
1/15/2=1/30+1/u
2/15=1/30+1/u
1/u=2/15-1/30
1/u=1/10
U=10cm