On a 120 km track a train travels the first 30 km at a uniform speed of 30 km/h . calculate the speed with which the train should move rest of the track so as to get the average speed of 60 km/h for the entire trip
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Average speed is equal to :
Total distance ÷ total time
Total distance = 120 Km
Let total time = t
60 = 120 / t
60t = 120
t = 2 hrs
Time taken to cover 30km is :
30 /30 = 1hr
2 - 1 = 1hr
The distance covered in the remaining one hr is :
120 - 30 = 90
Speed is thus :
90/1 = 90km/h
Total distance ÷ total time
Total distance = 120 Km
Let total time = t
60 = 120 / t
60t = 120
t = 2 hrs
Time taken to cover 30km is :
30 /30 = 1hr
2 - 1 = 1hr
The distance covered in the remaining one hr is :
120 - 30 = 90
Speed is thus :
90/1 = 90km/h
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ANSWER
In the first 30 km speed of the train, v1 = 30 km/h
Speed of the train in the next 90 km, v2 (to be determined)
Average speed = 60 km/h = (v1 + v2)/2
= (30 km/h + v2)/2
→ v2 = 90 km/h
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