For the situation as shown in the figure, find the velocity of image formed by the mirror

For first refraction through lens,  u=−30cm,f=+20cm ∵1v−1u=1f ∴v=+60cm vimage lens=v2u2dudt=602−3026−2Or    vimage−vlens=16cms−1 ∴vimage=16+2=18 cms−1Image formed by lens will act as object  for the mirror hence the object distance for the mirror is equal to u 'For reflection through mirror,  u'=−(80-60)=-20cm,f'=−10cm ∴v'=−20cm ∴vimage mirror=−−202−20218−4=−14cms−1 ∴vimage =−14+4=−10cms−1