A paticle of mass m is projected vertically upwards with speed U. The air resistance produces a retarding force mkv^2 , where k constant and v the speed of the particle. Find the greatest height reached by the particle. Determine the speed W with which the particle will return to the point of projection. I have done the first part of this question using a=-g-kv^2 I found the greatest height reached to be (U^2(g-kv^2)) / 2g^2 i think i have done this right! I am unsure how i then find the speed W?? Do i take downward motion as i new problem, so that when the particle is at greatest height t would=0?? Please help!