Question

Abdul, while driving to school ,computes the speed for his trip to be $20km{h}^{-1}$.On his return trip along the same route there is less traffic and the speed is $30km{h}^{-1}$.What is the average speed for abdul's overall trip?

Answer 1

Let the distance between school and home is $s$.

While going -

$t_1=\frac{s}{v_1}$

And while returning-

$t_2=\frac{s}{v_2}$

Total distance =$2s$ and total time is $t=t_1+t_2$

$v_{av}=\frac{2s}{t}=\frac{2s}{\frac{s}{v_1}+\frac{s}{v_2}}$

$⟹v_{av}=\frac{2v_1{v}_2}{v_1+v_2}$

$⟹v_{av}=\frac{2\times 20\times 30}{20+30}$

$⟹v_{av}=24km/h$