Question

Find the velocity of image at given instant in vector format, f equal to 15cm and object placed 20cm away from mirror and height from principal axis is 2cm

Answer 1

1/u+1/v=1/f

but v=2/3*u

1/u+1/2/3u=1/f

1/u+3/2u=1/f

1+6/u=1/f

7/u=1/f

but,u=20

7/20=1/f

Take the reciprocal

f=20/7cm