2.5 a,\(\Rightarrow v=\dfrac{S}{t}=\dfrac{200}{4}=50km/h\)(do thi van toc co dang la 1 duong thang song song vs Ox thoi, ban tu ve)
b,\(\Rightarrow x=50t\left(km,h\right)\)
xet \(\left\{{}\begin{matrix}t=0\Rightarrow x=0\\t=1\Rightarrow x=50\end{matrix}\right.\)\(\Rightarrow A\left(0,0\right);B\left(1;50\right)\) roi ve do thi theo A,B
c,\(\Rightarrow S=50.3=150km\) cach A 150km, di duoc 150km
d,\(\Rightarrow120=50t\Rightarrow t=2,4h\)=>luc 8h24'
2.6
a,\(\Rightarrow\left\{{}\begin{matrix}xA=60t\\xB=15+50t\end{matrix}\right.\)\(\left(km,h\right)\)
b, gap nhau \(\Rightarrow xA=xB\Rightarrow t=1,5h\) vi tri gap nhau cach A: \(xA=90km\)
c,\(\Rightarrow d=\left|60-15-50\right|=5km\)
d,\(\Rightarrow\left|xA-xB\right|=3\Leftrightarrow\left|60t-15-50t\right|=3\Rightarrow\left[{}\begin{matrix}t=1,8h\\t=1,2h\end{matrix}\right.\)
2.2
a,\(\Rightarrow t=\dfrac{S}{v}=\dfrac{1800}{600}=3h\)
b,\(\Rightarrow3-\dfrac{20}{60}=\dfrac{1800}{v'}\Rightarrow v'=675km/h\)
c,\(\Rightarrow t''=\dfrac{S}{v''}=\dfrac{1800}{500}=3,6h\)\(\Rightarrow t\uparrow0,6h\)
2.3 a,\(\Rightarrow vtb=\dfrac{S}{\dfrac{\dfrac{1}{3}S}{30}+\dfrac{\dfrac{1}{3}S}{20}+\dfrac{\dfrac{1}{3}S}{10}}=\dfrac{S}{\dfrac{S}{90}+\dfrac{S}{60}+\dfrac{S}{30}}=\dfrac{\left(90.60.30\right)S}{S\left(60.30+90.30+60.90\right)}=\dfrac{180}{11}km/h\)
2.4 \(\Rightarrow v=\dfrac{2.40+1,5.50+0,5.35}{4}=43,125km/h\)
bạn đăng từng câu nhỏ lên mình làm giúp nha =)))
