Question

if a train 100 m long takes 10 seconds to cross a telegraph post, then how much time does it take to cross a bridge of length 100 m

Answer 1

in the other way the train takes 10 sec to completely cross 100 m
therefore speed = dist/ time= 100/10=10 m per sec
now time taken to cross 100 m will be the same
10 sec as t= dist/ speed= 100/10= 10 sec

Answer 2

The time taken is 20 seconds.

Step-by-step explanation:

We are given that the 100 m train takes 10 s to cross a telegraph post which is a stable point.

This means that the train takes 10 s to completely cross 100 m.

Using the relation between distance, speed and time, we have the speed of the train as:

$\text{Speed}=\frac{\text { Distance }}{\text { Time }}=\frac{100}{10}=10 \mathrm{m} / \mathrm{s}$

As a result the time taken to cross a bridge of length 100 m would mean that the time taken to cross the two end points of the bridge that are 100 m apart.

That results in the total distance covered by the 100 m train as 100 + 100; which is 200 m

Hence, the time taken to cross the bridge is:

$\frac{200}{10} = 20 \ s$