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Question
A car travels 100 km at a speed of 60 km/h and returns with a speed of 40 km/h. Calculate the average speed for the whole journey.
Solution
In the first case, the car travels at a speed of 60 km/h for a distance of 100 km.
Thus,
`"Time" = "Distance travelled"/"Speed"`
So , t1 = `100/60` hr
= `5/3` hr
In the second case, the car travels at a speed of 40 km/h for a distance of 100 km.
Thus,
`"Time" = "Distance travelled"/"Speed"`
So , t2 = `100/40` hr
= `5/2` hr
Total time taken :
= t1 + t2
= `5/3 + 5/2` hr
= `25/6` hr
Total distance travelled = 200 km
We can calculate average speed as:
`"Average Speed" = "Tatal Distance travelled"/"Time"`
Average speed for the entire journey :
= `"(200)(6)"/25`
= 48 km/hr
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