Here is the following problem: A box of mass m is dropped on a converyor belt that has constant velocity u. a) Let friction between box and belt be nu. How far does the box slide until the box is moving at with same speed of belt? b) What force F must be applied to the belt to keep it moving at constant speed after the box falls on it, and for how long? My problem is setting up the equations of moition..... a) doesn't this force F need to be known for part a? or do we just consider some other force F' where m a = F' - nu m g or is m a = (dp/dt) = m (dv/dt) + v (dm/dt) I am close or not can't get anything to work out.... I keep ending up with more unknowns in whatever setup i choose What am not seeing?