1. The problem statement, all variables and given/known data An object is placed 20cm from a converging lens of focal length 5cm. If the object moves towards the lens at a speed of 12cm/s, at what speed does the image move away from the lens? 2. Relevant equations 1/f=1/di+1/do v=d/t 3. The attempt at a solution Let's say the object moves... Do=do1+do2 Di=di2-di1 so if di+fdo/do-f vt=(fdo2/do2-f)-(fdo1/do1-f) However, both vi and ti are unknown, so how should I proceed?