Goi T1 va T2 la thoi gian 2 xe di tren quang duong AB
Ta co:voi xe 1:
t1=(S/2)/v1=S/2v1(t1,t2 la thoi gian xe 1 di tren quang duong AB)
t2=(S/2)/v2=S/2v2
T1=t1+t2=(S/2v1)+(S/2v2)=S(v1+v2)/2v1v2(ae tu tinh nha) (1)
voi xe 2:
v1.(T2/2)+v2(T2/2)=S
=>T2/2(v1+v2)=S
=>T2=2S/(v1+v2) (2)
Lay (1)-(2) ta co
T1-T2=(S(v1+v2)/2v1v2)-2S/(v1+v2)
=>T1-T2=S(v1-v2)^2/((2v1v2)(v1+v2)) (ae tu tinh minh lam nhanh nha)
Ta thay T1-T2>0
=>v1=v2 thi 2 xe den cung luc
=>v1 khac v2=>t1>t2 =>xe 2 den truoc
goi ΔT la chenh lech thoi gian cua 2 xe
Doi 6 ph=1/10 h
Ta co:
ΔT=S(v1-v2)^2/((2v1v2(v1+v2))
1/10=S(50-30)^2((2.50.30)(50+30))=>1/10=S.1/600=>S=60(km)
=>T1=1,6h
T2=1,5h