Question

putin ajutor va rog

Answer 1

$v_m=\frac{d_1+d_2}{t_1+t_2} ~(asta-i~formula~de~baza)\\ \\ Zice~in~enunt~ca~sunt~jumatati~de~drum~intreg,~deci~d_1=d_2.\\ \\ v_1=\frac{d}{t_1} ~si~v_2=\frac{d}{t_2} \\ \\ Deci,~t_1=\frac{d}{v_1} ~si~t_2=\frac{d}{v_2} \Rightarrow~t_1+t_2= \frac{d(v_1+v_2)}{v_1*v_2} \\ \\ Inlocuiesti~in~formula~de~baza:\\ \\ v_m=\frac{2d}{\frac{d(v_1+v_2)}{v_1v_2}} =\frac{2*v_1*v_2}{v_1+v_2} \\ \\ Acum,~pui~valorile~din~enunt:\\ \\ 48=\frac{2*v_1*60}{v_1+60} ~\Leftrightarrow~48*v_1+2880=120*v_1\\ \\ 72*v_1=2880 \\ \\ \Rightarrow~\boxed{v_1=40~km/h}$