Physics URGENT!!!
posted by Anonymous on .
Gayle runs at a speed of 9.00 m/s and dives on a sled, initially at rest on the top of a frictionless, snowcovered hill, that has a vertical drop of 20.0 m. After she has descended a vertical distance of 4.00 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 bottom of the hill?
Gayle’s mass is 70.0 kg, the sled has a mass of 2.00 kg, and her brother has a mass of 50.0 kg.

energies gained=final energy
HerPE+HisPE+herinitalKE+hisInitialKE= finalcombinedKE + finalPE
+G*9.8*20+B*9.8*16 +1/2 G 9^2+ 0=1/2 (G+B)Vf^2+0
G is her mass, B is brothers mass, Vf is the finalspeed at bottom.
check my thinking. 
I don't think I am getting the right value, what are you getting?