A train starting from rest first accelerates uniformly up to a speed of 80 km/h for time t, then it moves with a constant speed for time 3t. The average speed of the train for this duration of journey will be (in km/h) :

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Solution

Q.
A train starting from rest first accelerates uniformly up to a speed of 80 km/h for time t, then it moves with a constant speed for time 3t. The average speed of the train for this duration of journey will be (in km/h) : [2024]

1 30

2 80

3 40

4 70

Ans.
(4)

$Average speed = \frac{Distance}{Time} = \frac{\frac{1}{2} (t) (80) + 80 \times 3 t}{4 t}$

$V_{av} = \frac{40 t + 240 t}{4 t} = \frac{280}{4} = 70 km/hr$

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