Ta có :
\(\left\{{}\begin{matrix}s_1=s_3\\t_1=t_2\end{matrix}\right.=>\left\{{}\begin{matrix}v_1t_1=v_3t_3\\t_1=t_2=\dfrac{v_3}{v_1}.t_3\end{matrix}\right.\)
\(v_{tb}=\dfrac{s_1+s_2+s_3}{t_1+t_2+t_3}=\dfrac{2s_1+s_2}{2t_1+t_3}=\dfrac{2v_3t_3+\dfrac{v_2.v_3.t_3}{t_1}}{\dfrac{2v_3t_3}{v_1}+t_3}\)
\(=\dfrac{2.60+\dfrac{45}{30}.60}{\dfrac{2.60}{30}+1}=42\left(\dfrac{km}{h}\right)\)
Vậy vận tốc trung bình trên cả quãng đường alf 42 km/h
Vận tốc trung bình là:
\(\dfrac{30+45+60}{3}=45\) (km/h)
Tóm tắt:
\(v_1=30\) km/h
\(v_2=45\) km/h
\(v_3=60\) km/h
____________________
\(v_{tb}\)= ? km/h
Giải:
Vận tốc trung bình là:
\(v_{tb}=\dfrac{v_1+v_2+v_3}{3}=\dfrac{30+45+60}{3}=45\) km/h
Vậy;................................................
Tóm tắt :
\(v_1=30km/h\)
\(v_2=45km/h\)
\(v_3=60km/h\)
\(v_{tb}=?\)
BL :
\(v_{tb}=\dfrac{s_1+s_2+s_3}{t_1+t_2+t_3}=\dfrac{s_1+s_2+s_3}{\dfrac{s_1}{v_1}+\dfrac{s_2}{v_2}+\dfrac{s_3}{v_3}}=\dfrac{s_1+s_2+s_3}{\dfrac{s_1}{30}+\dfrac{s_2}{45}+\dfrac{s_3}{60}}\)
Áp dụng vào tính nhé !