Question

Va rog frumos sa ma ajutati! Imi trebuie urgent rezolvarea problemei!
Un automobil parcurge prima jumatate a drumului sau cu viteza de 54 km/ h,iar cealalta jumatate cu viteza de 20 m/ s.Cre este valoarea vitezei medii?
Dau punctaj Maxim!

Answer 1

$d=d_1+d_2$

$d_1=d_2=\frac{d}{2}$

$t1=\frac{d_1}{v_1}=\frac{\frac{d}{2}}{v_1}=\frac{d}{2v_1}$

$t_2=\frac{d_2}{v_2}=\frac{\frac{d}{2}}{v_2}=\frac{d}{2v_2}$

$t=t_1+t_2$

$v_{med}=\frac{d}{t}$

$v_{med}=\frac{d}{\frac{d}{2v_1}+\frac{d}{2v_2}}$

$v_{med}=\frac{d}{\frac{d(v_1+v_2}{2v_1v_2}}$

$v_{med}=\frac{2dv_1v_2}{d(v_1+v_2)}$

$v_{med}=\frac{2v_1v_2}{v_1+v_2}$

$54\frac{km}{h}=15\frac{m}{s}$

$v_{med}={2*15*20}{15+20}=\frac{600}{35}=17,14\frac{m}{s}$