12.
d₁=d/2
d₂=d/2
d₁+d₂=d
t=t₁+t₂
d₁=d/2=v₀t₁+at₁²/2 (*)
d₂=d/2=v₁t₂+at₂²/2 (1)
v₁=v₀+at₁ (2)
Din (1) si (2)=>d/2=v₀+at₁)t₂+at₂²/2 (**)
Din (*) si (**)=>a=d(t₁-t₂)/[t₁t₂(t₁+t₂)]=450(25-20)/[25*20(25+20)]=450*5/(500*45)=0,1 m/s²
v₀=(d-at₁²)/2t₁=(450-62,5)/50=7,75 m/s
vm=d/t=450/(25+20)=10 m/s
13.
vm=108 km/h=30 m/s
vm=at₁=>t₁=vm/a=30/1=30 s
d₁=at₁²/2=1*900/2=450 m
t'=t/2=2/2=1 min=60 s
d₂=vm*t'=30*60=1800 m
d=2d₁+d₂=900+1800=2700 m
