V1=72km/h=1.2km/min
S1=V1*t1=1.2*20=24km
V2=15m/s=0.9km/min
t2=S2/V2=27/0.9=30min
总时间t=t1+t2=20min+30min=50min
总路程S=S1+S2=24km+27km=51km
全程平均速度为
V=S/t=51km/50min=1.02km/min=17m/s=61.5km/h
V1=72km/h=1.2km/min
S1=V1*t1=1.2*20=24km
V2=15m/s=0.9km/min
t2=S2/V2=27/0.9=30min
总时间t=t1+t2=20min+30min=50min
总路程S=S1+S2=24km+27km=51km
全程平均速度为
V=S/t=51km/50min=1.02km/min=17m/s=61.5km/h