between 2 stations a train accelerates uniformly at first then moveswith constant speedand finally retards uniformly. if ratio of time taken be 1:8:1 AND THE MAXIMUM Speed attained is 60km/hr then find the average speed of train over complete journey?

Asked by Mansi Rathod | 19th Oct, 2013, 12:43: AM

Expert Answer:

The maximum speed attained by the train is 60 km/h.
 
So, the average speed during the constant speed motion will be 60 km/h.
 
Now, while acceleratting, train starts from rest and attains 60 km/h final speed.
Thus, average speed during acceleration is
 
(Vf + Vi)/2 = 60/2 = 30 km/h.
 
Similarly, while decelerating, initial speed will be 60 km/h and final speed will be 0.
Thus, average speed will be
 
(Vf + Vi)/2 = 60/2 = 30 km/h.
 
The ratio of time taken for each motion is 1 : 8 : 1. Let us say that is time for acceleration is 1 hour and deceleration is 1 hour, then constant speed will be for 8 hours.
 
Thus, average speed over entire journey is
 

Answered by Romal Bhansali | 21st Oct, 2013, 10:22: AM

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