An object is placed at a distance of 40cm from a concave mirror of focal length 15cm. If the object is displaced through a distance of 20cm towards the mirror, the displacement of the image will be

Using mirror formula,1f=1v1+1u;-115=1v1-140⇒1v1=1-15+140v1=-24 cmWhen object is displaced by 20 cm  towards mirror. Now,u2=-20 cm1f=1v2+1u2;1-15=1v2-120⇒1v2=120-115v2=-60 cmSo, the image will be shift away from mirror by (60-24)cm=36 cm