2014-06-21 22:46:35 補充:
Assume both ballons have v=10 at first
Iron and plastic has 10 and 5 units of mass
both minus 20 J for air resistance
for v=10,
E(Ir)=500J
E(pl)=250J
After 20J reduction,
480=1/2 m(Ir)v(Ir)^2
v(Ir)=root 96
230=1/2 m(pl)v(pl)^2
v(pl)=root 92
Iron ballon is moving faster