Physics URGENT!!!
posted by Anonymous .
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. (a) What is the sled’s speed just after jumping on the sled? (b) What is the sled’s speed just before her brother jumps on? (c) What is the speed of the sled just after the brother jumps on? (d) 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

m=2 kg , m1=70+2=72 kg, m2= 50 kg
v =9 m/s, Δh=4 m, h=20 m
(a)
m1•v =(m1+m)v1
v1= m1/(m1+m)
(b) KE1+ΔPE=KE2
(m1+m)•v1²/2+(m1+m)•g•Δh=(m1+m)•v2²/2
v2=sqrt(v1²+2g•Δh)
(c) (m1+m)•v2= (m1+m2+m) • v3
v3 = (m1+m)•v2/(m1+m2+m)
(d) (m1+m2+m)•v3²/2+ (m1+m2+m)g(h Δh) = (m1+m2+m)v4²/2
v4=sqrt{ v3²/2+2 g(h Δh)}. 
Can you give me the values you got so I can check mine?
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