SOLUTION: 225 metre long train is running at a speed of 60 km/h and a boy on the ground is running at a speed of 6 km/h. How long will the train take to pass the boy if they ae running in th
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Question 956638: 225 metre long train is running at a speed of 60 km/h and a boy on the ground is running at a speed of 6 km/h. How long will the train take to pass the boy if they ae running in the same direction and also in the oppsite diection?
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
Start at point A with the head of the train at
point A and the boy at point A
---------------------------------
Make point B where the boy is when the tail end
of the train is also at point B
---------------------------------
Let = the distance in km from A to B
Let = time in hrs for the boy and the tail end
of the train to get to B
---------------------------------
Both going in the same direction:
The equation for the boy is:
(1)
Equation for the train:
(2)
--------------------
Substitute (1) into (2)
(2)
(2)
(2) hrs
Convert to seconds:
sec
The train will pass the boy in 15 sec
=================================
In the opposite direction, the boy at A
turns around and runs toward the tail
end of the train when the head is at A
-----------------------------------
You can think of this as the boy standing
still and the train coming toward him at
the sum of their speeds
-----------------------------------
The distance is km
hrs
Convert to seconds
sec
The boy and the tail end of the train
will meet in 12.273 sec
--------------------------------
check:
Boy's equation:
km
train's equation:
km
-----------------------
OK
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