A girl runs at a speed of around 4.00 m/ s and dives to a sled primarily at rest on the top of the frictionless, snowy hill. After she has descended a vertical distance of 5.00 m, her little brother hops on her back and altogether they continue down the hill. Determine their speed at the bottom of the hill when the vertical drop is 15.0 m? The girls mass is around 50.0 kg, the boys mass is around 30.0 kg, and the sleds mass is around 5.00 kg.