Question

EXAMPLE 7. When the engine of an electric train 72 m long passes a stationery car,
its speed is 6 m sl. When the tail end of the train passes the same car, its speed is 9 ms.
What is the acceleration of the train and what time does it take to pass the car ?​

Answer 1

Answer:

9.61 sec

Explanation:

The train is moving with an acceleration a, so the engine of train passes the stationary car with an initial speed u, and the tail of train passes the same car with a different speed, v.



So,using the third equation of motion

v2-u2 = 2aS 

S is the distance travel= length of train = 72 m

Given, v= 9 m/sec and u= 6 m/sec

(9)2 -(6)2= 2×a×72

So, acceleration a, =0.3125 m/sec2

Now, using first equation of motion,we get time t

v=u+a×t

9=6+0.3125×t

and t= 9.61 sec

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