Question 1195335
A train T1 moving at an average speed of 90 km/h takes 8 seconds to completely cross a bridge that is 80 meters long.
 Another train T2 which is 155 meters long and moving in the opposite direction on a parallel track at an average speed of 108 km/h is just beginning to pass trainT1.
 Calculate the time in seconds that it takes for the two trains to completely pass one another. 
:
Train 1: Find the distance, in meters, it travels in 1 sec at 90 km/h
m/sec = {{{(90000/3600)}}}
m/s = 25 m/sec
then
8 * 25 = 200 meters in 8 sec
The bridge is 80 meters so the train is 200-80 = 120 meters long
:
Train 2: 
Find the dist in meters the train travels in 1 sec at 108 km/h
m/s = {{{108000/3600}}}
m/s = 30 meters per sec
The relative speed when the two trains meet each other: 30 + 25 = 55 m/sec
:
"Calculate the time in seconds that it takes for the two trains to completely pass one another"
{{{(120+155)/55}}} = 5 seconds