not really. specific homework questions, more like, needing help to get started. There are a few things I'm having difficulty understanding.. 1)how to determine what is Ei and what is Ef. i.e. if a ball is shot into a net with an initial speed of 5m/s at a height of 2m, what speed will the ball travel into the net at a height of 3m? from what i learnt: Eti=Etf Eki + Eg = Ekf + Egf .. I don't get why though.. cause then theres stuff like; a mass is placed on level drictionless surface, and is released of a spring attached to the side of the wall. so the energy here would be Eei=Ek+Eef.. so theres no gravity here? and when the spring is compressed towards the wall, its still considered elastic energy? 2) a 50 kg crate is pulled 40 m along a horizontal floor by a constant applied force of 100 N, the floorr exerts a force of 50N on the crate. how much work is done on the crate by the floor. the equation we used was W=Fcos#*d ... but why would we sub in 40 m into d? the frictional force didn't push the mass to 40 m.. if more, it'd be restricting it from travelling it more than 40, so it shud be pulling back a certain distance to keep it at 40, not making it 40m itself..