D 1/3alpha + 1/2beta +gama
C vC > vB > vA
D The collision is elastic because both momentum and kinetic energy are conserved in the collision.
C K<Ug< E
C T2/T1 = 2
B 上升到6，平到8
D tau2>tau3=tau4>tau1
B 30N 飞船飞到球
B f1
B 6m/s 0m/s
C -A 到A余弦函数
DCDBC
BDCDB
BDBAA
BACBC
ABDCD
CBAAA
BCCDA
BCDAD