Question

9.
On a 200 km track, a train travels the first 50 km
at a uniform speed of 40 km/h. How fast the train
must travel the next 150 km so as to maintain the
average speed of 60 km/h for the whole journey?
​

Answer 1

Answer:

7.2 km/h

Explanation:

let the speed during the second part be x

av speed= total distance over time

total distance = 200km

t = d/s

t1 = 50/40

t2 = 150/x

total time = t1+t2

= 5/4+150/x

= 5x+600/4x

given average speed = 60

60 = 200/(5x+600/4x)

60 = 800x/5x+600

300x + 3600 = 800x

3600 = 500x

x = 3600/500

x = 7.2 km/h