Question

A motorcyclist drives from place A to B with a uniform speed of 30 km h^-1 and returns from place B to A with a uniform speed of 20 km h^-1. Find his average speed.

Answer 1

We have to find the average velocity of the entire journey. For this, we have the following information :
Speed from A to B = (v₁) = 30 m/s
Let the distance from A to B be  (d).
Also, let the time taken to travel from A to B be (t₁).
`"Time" = "Distance travelled"/"Speed"`
we have : 
t₁ = `d/30`

Speed from B to A (v₂) = 20 m/s
Let the time taken to travel from B to A be (t₂).
Thus, we have :
t₂ = `d/20`
Total time of journey : 
= t₁ + t₂

= `d/30 + d/20`

= `d/12`
Total distance travelled is 2d.
Therefore,
`"Average speed" = "Total distance travelled"/"Time"`
On putting the values to obtain the average speed of the motorcyclist, we get :
= `"(2d)12"/d`
= 24 km/hr