Question

Example 7. On a 120 km road, a car travels the
first 30 km at a uniform speed of 30 km h-1. How
fast must the car travel for the rest of track so
as to have an average speed of 60 km h-1 for the
entire journey?
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Answer 1

Answer

On a 120 km road, a car travels the first 30 km at a uniform speed of 30 km/hr. How fast must the car travel for the rest of the track to have an average speed of 60 km/hr for the entire journey?

Total distance to be covered = 120 Km

Overall average speed for the entire journey = 60 Km/hr

Overall average speed = Total distance / total time taken

60 Km/hr = 120Km / total time

therefore, the total time required = 120 Km / 60 Km/hr = 2 hrs

For the first part of the journey,

30 Km was covered at an average speed of 30 Km/hr,

Time taken = Distance / speed = 30 Km / 30 Km/hr = 1 hr

For the second part of the journey,

Distance left = 120 Km - 30 Km = 90 Km

Time left = Total time - Time taken by first part of the journey

Time left = 2 hrs - 1 hr = 1hr

The average speed required for the second part of the journey to achieve an overall average speed of 60 Km = Distance left / Time left = 90 Km / 1 hr = 90 Km/hr

Explanation:

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