[tex]t_1=t_{2[/tex]
[tex]v_1=15 m/s[/tex]
[tex]v_2= 90 km/h= 90000m/3600s=25 m/s[/tex]
[tex]v_m= \frac{d_1+d_2}{t_1+t_2} [/tex]
[tex]v= \frac{d}{t} ==\ \textgreater \ d=v*t[/tex]
[tex]d_1=v_1*t_1=15t_1[/tex]
[tex]d_2=v_2*t_2= 25t_1[/tex]
[tex]v_m= \frac{15t_1+25t_1}{2t_1} = \frac{40t_1}{2t_1} =20m/s[/tex]
[tex]d_1= \frac{d}{2} [/tex] [tex]d_2= \frac{d}{2} [/tex] [tex]d_1+d_2=d[/tex]
[tex]v_1=54 km/h =54000m/3600s=15 m/s[/tex] [tex]v_2=25 m/s[/tex]
[tex]v_m= \frac{d_1+d_2}{t_1+t_2} [/tex] [tex]v= \frac{d}{t} ==> t= \frac{d}{v} [/tex]
[tex]t_1= \frac{ \frac{d}{2} }{15} = \frac{d}{30} [/tex]
[tex]t_2= \frac{ \frac{d}{2} }{25} = \frac{d}{50} [/tex]
[tex]v_m= \frac{d}{\frac{d}{30}+\frac{d}{50}} [/tex]
[tex]v_m= \frac{d}{\frac{5d+3d}{150}}[/tex]
[tex]v_m= \frac{d}{\frac{8d}{150}[/tex]
[tex]v_m= \frac{150}{8}[/tex]
[tex]v_m= 18.75[/tex]
