on the 100 m track , a train travels the first 30 km at the uniform speed of 30 km/h. how fast must the train travel the next 70 km so as to average 40km/h for the entire trip?

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on the 100 m track , a train travels the first 30 km at the uniform speed of 30 km/h. how fast must the train travel the next 70 km so as to average 40km/h for the entire trip?

2

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The velocity of the train should be 45.55 km/hr

it would be v = s / t =>30 = 30 / t

t = 1 hr

For next 70 km

let velocity be x

v = s / t

x = 70 / t

t = 70 / x

hence total time taken is 1 + 70/ x = (70 + x) / x

total dist. travelled is given i.e. 100km

hence avg. velovity = total dist / total time

40 = 100 divided by (70 + x) / x

40. (70+x) / x = 100

2800 + 40x - 100x = 0

- 60x = - 2800

x = - 2800 / -60

x = 45.55 km/hr