1. The problem statement, all variables and given/known data Gayle runs at a speed of 4.20m/s and dives on a sled, which is initially at rest on the top of a frictionless snow-covered hill. After she has descended a vertical distance of 4.77m, her brother, who is initially at rest, hops on her back and together they continue down the hill. What is their speed at the bottom of the hill if the total vertical drop is 17.4m? Gayle's mass is 50.8kg, the sled has a mass of 5.50kg and her brother has a mass of 33.7kg. 2. Relevant equations conservation of momentum: m1v1+ m2v2 = m1+m2(v3) conservation of energy: KE1 + PE1 = KE2 + PE2 3. The attempt at a solution I tried using conservation of momentum to find the velocity of Gayle+sled, then used that to find Gayle+sled's PE and KE at a vertical distance of 12.63m --> total energy of the system. That's when things become fuzzy... are we supposed to include the potential energy of Gayle's unmoving brother within the system? (In which case to find the final velocity at the bottom of the hill, PE of both her and her brother = zero, and KE of Gayle+sled+brother = total energy of the system?) Any help would be incredibly appreciated!