Question

A train 471 m long is moving on a straight track with a speed of 75.1 km/h. The engineer applies the brakes at a crossing, and later the last car passes the crossing with a speed of 15 km/h. Assuming constant acceleration, determine how long the train blocked the crossing. Disregard the width of the crossing. Answer in units of s.

Answer 1

`t = 37.6 s`

Step-by-step explanation:

As we know that train is initially moving with the speed

`v_i = 75.1 km/h`

now we know that

`v_i = 20.86 m/s`

now the final speed of the train when it crossed the crossing

`v_f = 15 km/h`

`v_f = 4.17 m/s`

now we can use kinematics here

`v_f^2 - v_i^2 = 2 a d`

`4.17^2 - 20.86^2 = 2 a(471)`

`a = -0.44 m/s^2`

Now the time to cross that junction is given as

`v_f - v_i = at`

`4.17 - 20.86 = a(-0.44)`

`t = 37.6 s`