A person travels along a straight road for half of the distance with a velocity 60km/h and the remaining half distance with a velocity  80km/h. Then the average velocity is given by………

Given that  $s_1=\frac{s}{2}{s}_2=\frac{s}{2}$
$v_1=60km/h$
$v_2=80km/h$
$\therefore$ Time taken to cover first half of the distance  $t_1=\frac{s}{2v_1}$
Time taken to cover second half of the distance  $t_2=\frac{s}{2v2}$
Average velocity  $\left(\overline{v}\right)=\frac{Totaldisplacement}{Totaltime}$
$\begin{array}{l}=\frac{s_1+s_2}{t_1+t_2}\\ =\frac{\frac{s}{2}+\frac{s}{2}}{\frac{s}{2v_1}+\frac{s}{2v_2}}=\frac{2v_1{v}_2}{v_1+v_2}\\ =\frac{2\times 60\times 80}{60+80}\\ =\frac{120\times 8}{14}\\ =68.57\mathrm{km}/\mathrm{h}\end{array}$