gayle runs at a speed of 4.00 m/s and dives on a sled, initially at rest on the top of a frictionless, snow-covered hill. after she has descended a vertical distance at a 5.00 m, her brother,who is initially at rest, hops on her back, and they continue down the hill together, what is their speed at the buttom of the hill if the total vertical drop is 15.0 m? gayle's mass is 50.0 kg, the sled has a mass of 5.00 kg, and her brother 's mass is 30.0 kg.