A train travels a certain distance d in a straight line at a constant speed of 60 km/h, and then travels another distance equal to 2d in the same direction at a constant speed of 80 km/h. What is the train's average speed for the entire journey?
Answer (1)
3rd Nov, 2021
The time t1 to cover distance d at a speed of 60 km/h is by t1 = d / 60
The time t2 to cover distance 2d at a speed of 80 km/h is t2 = 2d / 80
Average Speed = distance/time
= (d + 2d) / (d/60) + (2d/80)
= 3d / (80d + 2d×60)/ (60×80)
= 3 d/(200d/4800)
= 3d (4800)/200d
= 72 km/h
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