Question:
When an engine of an electric train 72m long passes a stationary car, it's speed is 6m/s. When the tail end of the train passes the same car, it's speed is 9m/s. What is the acceleration of the train and what time does it take to pass the car.
Answer:
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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