SOLUTION: A train moving at uniform speed takes 20 seconds to pass a cyclist riding at 11 km/hr but only 9 seconds to pass a post. find its length.

Question 483854: A train moving at uniform speed takes 20 seconds to pass a cyclist riding at 11 km/hr but only 9 seconds to pass a post. find its length.
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
A train moving at uniform speed takes 20 seconds to pass a cyclist riding at 11 km/hr but only 9 seconds to pass a post.
find it's length.
:
change 11 km/hr to meter/sec
= 3.056 m/sec
:
Let L = length of train in meters
Let s = speed of train in m/sec
:
Using the post as ref:
L = 9s is the length of the train in meters
:
Using the bike going 3.056 m/sec, as ref
L = 20(s - 3.056) is the length of the train
:
We can find s:
20(s - 3.056) = 9s
20s - 61.11 = 9s
20s - 9s = 61.11
11s = 61.11
s =
s = 5.56 m/sec is the speed of the train
then
9 * 5.56 = 50 meters is the length of the train (post as ref)
and
20(5.56-3.056) ~ 50 meters also using a moving bike as ref
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