Question

||On a 100 km track, a train travels the first 30 km at a uniform speed of
* 30 km/hr. How fast must the train travel the next 70 km so as to average 40 km h-1 for
the entire trip?||
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¶Class 9 Motion Chapter¶ ​

Answer 1

Answer:

46.67 km/h

Explanation:

for the first 30 km, time t1 = 30/30 = 1 hour

for the next 70, let the speed be x

therefore t2 = 70/x

we know total distance = 100km (given)

average speed = 40km/h (given)

to find average speed, we use average speed = total distance / total time

total time = t1 + t2

1+70/x = x+70/x

therefore,

40 = 100/(x+70/x)

40 = 100x/(x+70)

40x + 2800 = 100x

60x = 2800

x = 46.67 km/h

check

100/ 1+70/46.67 = 40

100(46.67)/46.67+70 = 40

4667/116.67 = 40

40 = 40