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

Solution

## The correct option is C $$40km/h$$Lets consider, $$x=$$ distance covered by the busA bus covered $$x$$ distance with speed $$30km/h$$,$$t_1=\dfrac{x}{30}hr$$Bus returned to origin with  speed $$60km/h$$,$$t_2=\dfrac{x}{60}hr$$The average speed for the entire journey is$$v_{avg}=\dfrac{Total\, distance}{Total\, time}$$ $$v_{avg}=\dfrac{2x}{t_1+t_2}$$$$v_{avg}=\dfrac{2x}{\dfrac{x}{30}+\dfrac{x}{60}}$$$$v_{avg}=\dfrac{2x}{0.05x}$$$$v_{avg}=40km/h$$The correct option is C.Physics

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