Question

un mobil parcurge jumatate din distanta ce o are de parcurs cu v1=200km/h iar cealalta jumatate cu v2=300km/h. in cit timp parcurge aceasta distanta ? distanta totala de parcurs este D=800km.

Answer 1

Parcurge 400 km cu v1, adica t=d/v=400/200=2h.

Parcurge 400 km cu v2, adica 400/300=1.33h.

In total, t=3.33h=200min.

Answer 2

D=d1+d2

d1=d2=D/2

t1+t2=t

t1=d1/v1=D/2/v1=D/2v1

t2=d2/v2=D/2/v2=D/2v2

vm=D/t=D/(D/2v1+D/2v2)=1/(v2+v1)/2v1v2=2v1v2/(v1+v2)=2•200•300/(200+300)=120000/500=240 km/h

t=D/vm=800/240=3,33 h