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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.
Solution
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
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