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CBSE Class 11-science Answered

the motors of an electric train give it an acceleration of 1m/s2 and the brks give a negavtive acceleration of 3m/s2. find the shortest time interval in which train can make a journey between two stations 1210m apart
Asked by Mansi Rathod | 19 Oct, 2013, 12:39: AM
answered-by-expert Expert Answer
The train starts from rest and accelerates to reach a maximum velocity v after which it starts decelerating.
 
Let s be the distance covered while accelerating and so (1210 - s) will be the distance covered while decelerating.
 
Hence, we have for acceleration
 
v2 = u2 + 2as = 2as              ...... (1)
 
And we have for deceleration
 
02 = v2 + 2d(1210 - s)
-v2 = -2d(1210 - s)
v2 = 2d(1210 - s)                 ...... (2)
 
From equations (1) and (2), we have
 
 
Now, using equation v  = u + at for both cases, we have
 
 
Answered by Romal Bhansali | 21 Oct, 2013, 09:56: AM

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