SOLUTION: Two trains 100 meters and 120 meters long are running in the same directions with speed of 72 km/hr and 54 km./hr. in how much time will the first train cross the second?

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Question 1036205: Two trains 100 meters and 120 meters long are running in the same directions with speed of 72 km/hr and 54 km./hr. in how much time will the first train cross the second?
Found 2 solutions by ikleyn, josmiceli:
Answer by ikleyn(52798) (Show Source):
You can put this solution on YOUR website!
.
Two trains 100 meters and 120 meters long are running in the same directions with speed of 72 km/hr and 54 km./hr.
In how much time will the first train cross the second?

Answer. = = 44 seconds.

Solution

What is 20 in the denominator in the Answer? It is 20 meters per second, which is the speed of the first train, 72 kilometers per hour, converted to meters per second. What is 15 in the denominator in the Answer? It is 15 meters per second, which is the speed of the second train, 54 kilometers per hour, converted to meters per second. What is the difference (20-15) in the denominator? It is the relative speed of the faster train to slower train moving on parallel tracks in the same direction. What is the sum (100+120) in the numerator? It is the sum of the lengths of the two trains. Why we divide (100+120) by (20-15)? It is the time required for the faster train to pass completely the slower train.

See the lesson A train passing another train in this site.

Answer by josmiceli(19441) (Show Source):
You can put this solution on YOUR website!
Start with the faster train's head lined up
with the slower train's tail
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Imagine that the slower train is not moving,
but the faster train moves at the sum of their
speeds
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The faster train has to cover the distance of
the sum of their lengths In hrs
-----------------------
( all units in km )

hrs
Multiply by number of sec in 1 hr

The 1st train crosses the 2nd in 8.571 sec