A train passes a pole in 10 secs & a bridge of length 2km in 110 secs. What is its speed?

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justaguide's profile pic

justaguide | College Teacher | (Level 2) Distinguished Educator

Posted on

Let us assume the length of the train is L m.

The train passes a pole in 10 seconds and a bridge of length 2 kilometers in 110 seconds.

The speed of the from the fact that it crosses a pole in 10 sec is L/10 m/sec.

When the train crosses the bridge it has to travel a distance equal to the sum of its length and that of the bridge.

This gives the speed of the train as (L + 2000)/110 m/sec

As the two speeds are equal L/10 = (L + 2000)/110

=> 11L = L + 2000

=> 10L = 2000

=> L = 200

The length of the train is 200 m.

Its speed is 20 m/sec.

qwertymak's profile pic

qwertymak | Student, Grade 10 | (Level 1) Honors

Posted on

While train is passing pole

Let length of train =x

Length of pole is negligible

=> Total distance=x

Time = 10 secs

=> Speed = Distance/Time= x/10 m/s

While train is passing station

Total distance = x + 2000 metre

Time = 110 sec

Speed = (x + 2000)/110

Assuming the  speed of train to be constant

=> x/10 = (x+2000)/110

=> 11x = x+2000

=> 11x -x = 2000

=> x = 2000/10 = 200 metres

=> Speed = x/10 = 200/10

=> Speed = 20 m/s

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