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# A train of length L is traveling at a constant velocity and passes a

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A train of length L is traveling at a constant velocity and passes a [#permalink]

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02 Jul 2010, 23:35
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A train of length L is traveling at a constant velocity and passes a pole in t seconds. If the same train travelling at the same velocity passes a platform in 3t seconds then what is the length of the platform:

A) 0.5 L
B) L
C) 1.5 L
D) 2 L
E) 3 L
[Reveal] Spoiler: OA

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Re: A train of length L is traveling at a constant velocity and passes a [#permalink]

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03 Jul 2010, 01:33
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A train of length L is traveling at a constant velocity and passes a pole in t seconds. If the same train travelling at the same velocity passes a platform in 3t seconds then what is the length of the platform:
A) 0.5 L
B) L
C) 1.5 L
D) 2 L
E) 3 L

Sol:
Length of train=Distance=L
time to cross the pole=time=t
so speed=L/t

new time=3t. so distance travelled= 3t*L/t = 3L

the distance is equal to train length L+platform length = 3L
so platform is 2L. ans is D.
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Re: A train of length L is traveling at a constant velocity and passes a [#permalink]

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03 Jul 2010, 12:08
appy001 wrote:
A train of length L is traveling at a constant velocity and passes a pole in t seconds. If the same train travelling at the same velocity passes a platform in 3t seconds then what is the length of the platform:
A) 0.5 L
B) L
C) 1.5 L
D) 2 L
E) 3 L

Sol:
Length of train=Distance=L
time to cross the pole=time=t
so speed=L/t

new time=3t. so distance travelled= 3t*L/t = 3L

the distance is equal to train length L+platform length = 3L
so platform is 2L. ans is D.

Ahh - very sneaky question! It's easy to forget that the entire train has to pass by the platform, so it travels the extra L distance.

Nicely done!

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Re: A train of length L is traveling at a constant velocity and passes a [#permalink]

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31 Oct 2014, 23:47
Hello from the GMAT Club BumpBot!

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Re: A train of length L is traveling at a constant velocity and passes a [#permalink]

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01 Nov 2014, 05:40
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shamikba wrote:
A train of length L is traveling at a constant velocity and passes a pole in t seconds. If the same train travelling at the same velocity passes a platform in 3t seconds then what is the length of the platform:
A) 0.5 L
B) L
C) 1.5 L
D) 2 L
E) 3 L

Speed = L/t = (L+P)/3t. So P = 2L

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Re: A train of length L is traveling at a constant velocity and passes a [#permalink]

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01 Nov 2014, 08:40
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The distance the train is traveling isn't just L, it's L plus the length of the pole. This question assumes that the length of the pole zero.

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Re: A train of length L is traveling at a constant velocity and passes a [#permalink]

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20 Dec 2014, 21:38
Length of pole is assumed 0. From case 1 we get the speed of the train =L/t
In case 2 we need distance =speed x time =L/t x 3t=3L, but this 3L is the total distance inclusive of the length of the train which is L. so length of the platform =3L-L=2L.
Hope this explanation helps.

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Re: A train of length L is traveling at a constant velocity and passes a [#permalink]

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21 Dec 2014, 19:41
Hi All,

This question can be solved by TESTing VALUES.

We're told that a train has a length of L and passes a pole in T seconds.

Let's TEST:
L = 3 (feet)
T = 2 (seconds)

Since the pole is NOT given a length, we have to assume that that value is negligible (and does NOT factor into the calculations).

So, the entire length of the train passes the pole in 2 seconds. Thus, it's traveling 3 feet every 2 seconds.

Next, we're told that this train passes a platform in 3T seconds. This means that the train travels 3(2) = 6 seconds and travels 3(3) = 9 feet.

Those 9 feet are made up of the train (3 feet) and the platform (9 - 3 = 6 feet).

The question asks us for the length of the PLATFORM. Using these VALUES, we know that the PLATFORM = 6 when L = 3.

[Reveal] Spoiler:
D

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Re: A train of length L is traveling at a constant velocity and passes a [#permalink]

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24 Jan 2016, 09:01
Hello from the GMAT Club BumpBot!

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A train of length L is traveling at a constant velocity and passes a [#permalink]

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24 Jan 2016, 15:06
let r=rate
let p=length of platform
L+p=(3t)(r)=3rt
(L+p)/3=rt
L=rt
(L+p)/3=L
L+p=3L
p=2L

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Re: A train of length L is traveling at a constant velocity and passes a [#permalink]

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24 Jan 2016, 22:46
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Expert's post
shamikba wrote:
A train of length L is traveling at a constant velocity and passes a pole in t seconds. If the same train travelling at the same velocity passes a platform in 3t seconds then what is the length of the platform:

A) 0.5 L
B) L
C) 1.5 L
D) 2 L
E) 3 L

Look at the question logically:

"A train of length L is traveling at a constant velocity and passes a pole in t seconds"
To cross a pole (which can be considered a point), why does the train take t secs? Because the whole length of the train has to cross it.

" If the same train travelling at the same velocity passes a platform in 3t seconds"
Why does the train take extra 2t secs now? Because of the length of the platform. So the length of the platform must be 2L.

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Re: A train of length L is traveling at a constant velocity and passes a [#permalink]

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16 Aug 2017, 11:56
shamikba wrote:
A train of length L is traveling at a constant velocity and passes a pole in t seconds. If the same train travelling at the same velocity passes a platform in 3t seconds then what is the length of the platform:

A) 0.5 L
B) L
C) 1.5 L
D) 2 L
E) 3 L

It's a very simple question..
So, Train of length L passes a pole in t seconds. Velocity of pole v= L/t

Now this train of length L passes platform of say length p passes in 3t seconds .
So, (L+p)= v (3t) = L/t(3t) 3L
-> p = 2L

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Re: A train of length L is traveling at a constant velocity and passes a [#permalink]

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16 Aug 2017, 11:59
shamikba wrote:
A train of length L is traveling at a constant velocity and passes a pole in t seconds. If the same train travelling at the same velocity passes a platform in 3t seconds then what is the length of the platform:

A) 0.5 L
B) L
C) 1.5 L
D) 2 L
E) 3 L

We can also analyse it and solve it in a very short span of time as VeritasPrepKarishma suggested...

Train of length L passes a pole in t seconds i.e. it covers L in t seconds.
So, in 3t seconds it covers 3L distance, out of which L is length of train and 2L is length of platform... very simple, isn't it? :)
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Re: A train of length L is traveling at a constant velocity and passes a   [#permalink] 16 Aug 2017, 11:59
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