a, Ta có : 80cm = 0,8 m = 0,0008 km
2s = $\frac{1}{1800}$ h
⇒ v1 = $\frac{80}{2}$ = 40 (cm/s)
v2 = $\frac{0,8}{2}$ = 0,4 (m/s)
v3 = $\frac{0,0008}{\frac{1}{1800} }$ = 1,44 (km/h)
b, s1 = 40 × ( 2 × 60 ) = 4800 (cm)
s2 = 0,4 × ( 2 × 60 ) = 48 (m)
s3 = 1,44 × ( $\frac{2}{60}$ ) = 0 , 048 (km)