2019-2020
1
( )
A 20s B 20s
C 20s D 20s
2 ab 4v v t
A 5v
tB ab 17v
C 2
t 2v D 2.5vt
3 m B( ) BC(
) AB A A 30
AB F1 F2 ( )
AF1mg
B
C F2mg
D F2mg
4 a b
( )
A
B
C a b
D
5 (BDS) (GPS)
(GLONASS) 2020
