Question

the point size image of a tall building is produced at a distance 10 cm from a concave mirror. find the image distance if the object is placed at the distance of 15 cm from the mirror,

Answer 1

1/f = 1/u+1/v
1/f - 1/u = 1/v
1/10-1/15 =1/v
15-10/10*15 = 1/v
5/150 = 1/v
1/30 = 1/v 
v = +30cm