
Let object be at a distance xcm from the pole. Then, distance of image from the pole will be =15−x.
Given:
Magnification, m=2=u−v
⇒2=−x−(15−x)
⇒2x=15−x
⇒3x=15⇒x=5cm
Now,
Distance of the image from the pole =15−x=15−5=10cm
Therefore, v=10cm
From mirror formula:
f1=v1+u1
=101+(−5)1=101−2=10−1
⇒f=−10cm