Hello, everyone. I'm new here at the forums, and I've got a little physics problem I'd like your input on: "A roller coaster reaches the top of the steepest hill with a speed of 6.0 km/h. It then descends the hill, which is at an average angle of 45 degrees and is 45 m long. What will its speed be when it reaches the bottom? (Assume the coefficient of kinetic friction = 0.12)" I believe this is intended to be an inclined plane problem, but I think that either the mass or the weight of the roller cart is necessary to determine the rate at which it accelerates down the hill. Is there some way of solving the problem with the information given or is it impossible to do so without somehow determining the mass of the cart? Thanks in advance. -Intrigue- PS It was hinted that we ought to convert km/h to m/s before attempting to solve the problem, but this does nothing to suggest the mass or the weight of the roller coaster. On an ideal coaster (without friction) it might be possible to calculate the weight of the cart based on its speed at the top of the hill with respect to the side it climbs before the descent (assuming that both sides are 45 meters long and at the same 45 degree angle) but the coefficient at the end of the problem assures the existence of at least some friction, so this idea doesn't work either. Please post your thoughts.