Question

A bus covers its onward journey with a constant speed of $30km/h$ and its return journey with a constant speed of $60km/h$. The average speed for its entire journey is

• A. $90km/h$
• B. $45km/h$
• C. $40km/h$
• D. $15km/h$

Answer 1

The correct option is C $40km/h$

Lets consider, $x=$ distance covered by the bus

A bus covered $x$ distance with speed $30km/h$,

$t_1=\frac{x}{30}hr$

Bus returned to origin with speed $60km/h$,

$t_2=\frac{x}{60}hr$

The average speed for the entire journey is

$v_{avg}=\frac{Totaldistance}{Totaltime}$

$v_{avg}=\frac{2x}{t_1+t_2}$

$v_{avg}=\frac{2x}{\frac{x}{30}+\frac{x}{60}}$

$v_{avg}=\frac{2x}{0.05x}$

$v_{avg}=40km/h$

The correct option is C.