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# The train crosses a man standing on a platform 150 mts long

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Intern
Joined: 28 Jan 2005
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The train crosses a man standing on a platform 150 mts long [#permalink]

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15 Mar 2005, 12:35
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

The train crosses a man standing on a platform 150 mts long in 10sec. and crosses the platform completely in 22 sec.Find the length of train and speed of train.

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Manager
Joined: 15 Feb 2005
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Location: Rockville

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15 Mar 2005, 12:48
assuming the man is at the end of the platform and the train is at the other edge of the platform;
the front of the train reaches him in 10 seconds therefore the trains speed is 15m/sec
it completely crosses the platform in 22 seconds
therefore assuming speed stays the same, (150+x)=15*22
train length should be 180 m
unless i am missing something

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Intern
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15 Mar 2005, 13:04
Lenght of train = l m
speed = v m/s

therefore, l/v = 10 s - (1)

also, (150 + l)/v= 22 s - (2)

thus, v = 150/12 m/s

from (1), l = 10v = 1500/12 m

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Manager
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15 Mar 2005, 14:02
amit_upasani@hotmail.com wrote:
Lenght of train = l m
speed = v m/s

therefore, l/v = 10 s - (1)

also, (150 + l)/v= 22 s - (2)

thus, v = 150/12 m/s

from (1), l = 10v = 1500/12 m

How did you conclude that (the bolded area)??
author of the question...is this the way the question is phrased?

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Intern
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15 Mar 2005, 15:14
Rupstar wrote:
amit_upasani@hotmail.com wrote:
Lenght of train = l m
speed = v m/s

therefore, l/v = 10 s - (1)

also, (150 + l)/v= 22 s - (2)

thus, v = 150/12 m/s

from (1), l = 10v = 1500/12 m

How did you conclude that (the bolded area)??
author of the question...is this the way the question is phrased?

pass a person in x sec = cover a distance equal to the length of the train in x sec

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VP
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15 Mar 2005, 21:48
I found some strange values, I think I lost myself somewhere
4.4km/h and 330m

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16 Mar 2005, 04:47
Length of train=L
speed of train=V

V=(L(man)+V(man)*t(man))-(L(platform)+V(platform)*t(platform))/t(man)-t(platform)

where L(man)=0
t(man)=10sec i.e. train takes 10 sec to pass
v(man)=0 stationary object
L(platform)=150
t(platform)=22sec i.e. train takes 22 sec to pass

V=(0-150)/(10-22)
= 12.5m/sec(ans)
To find the length of train:

V=(L+L(man))/t(man) + V(man)

12.5=(L+0)/10 + 0
L=125mts(Ans)

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16 Mar 2005, 04:47
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