SOLUTION: A train, x m long, takes 30 seconds from the time it first enters a tunnel that is 400 m long, until it is completely through the tunnel. A stationary ceiling light in the tunnel i

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Question 1094814: A train, x m long, takes 30 seconds from the time it first enters a tunnel that is 400 m long, until it is completely through the tunnel. A stationary ceiling light in the tunnel is directly above the train for 10 seconds. Find the value, in metres, of x.
a) 350 b) 250 c) 450 d) 200 e) 300
Found 2 solutions by josmiceli, greenestamps:
Answer by josmiceli(19441) (Show Source):
You can put this solution on YOUR website!
From the time the front enters until the
rear of the train exits, the train has traveled
miles in sec
Rate of train =
Rate =
The stationary light tells you that the rate
of the train is
I can say now:

The train is 200 m long
I get (d) for answer
Get another opinion if needed

Answer by greenestamps(13200) (Show Source):
You can put this solution on YOUR website!

It takes 10 seconds for the train to pass a stationary point, like the ceiling light. So it also takes 10 seconds for the whole train to pass the entrance to the tunnel.

Since it is 30 seconds from the time the train first enters the tunnel until it is completely through the tunnel, and since it takes 10 of those seconds for the end of the train to reach the beginning of the tunnel, there are 20 seconds left for the end of the train to reach the end of the tunnel.

Then, since it takes 10 seconds for the train to pass a stationary point, in those 20 seconds the train travels twice its length.

So twice the train's length is equal to the length of the tunnel, which is 400m; so the length of the train is 200m.