Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 29)
29.
A train travelling at 48 kmph completely crosses another train having half its length and travelling in opposite direction at 42 kmph, in 12 seconds. It also passes a railway platform in 45 seconds. The length of the platform is
Answer: Option
Explanation:
Let the length of the first train be x metres.
| Then, the length of the second train is |  |
x |  |
metres. |
| 2 |
| Relative speed = (48 + 42) kmph = | |
90 x | 5 | |
m/sec = 25 m/sec. |
| 18 |
 |
[x + (x/2)] | = 12 or | 3x | = 300 or x = 200. |
| 25 | 2 |
Length of first train = 200 m.
Let the length of platform be y metres.
| Speed of the first train = | |
48 x | 5 | |
m/sec = | 40 | m/sec. |
| 18 | 3 |
| (200 + y) x |
3 | = 45 |
| 40 |
600 + 3y = 1800
y = 400 m.
Discussion:
48 comments Page 5 of 5.
Prabir kumar kar said:
1 decade ago
12 sec is used to cross both the train from opposite direction.but 45 sec is used to pass only the platform by the fastest train.
Syndhya said:
1 decade ago
Could anybody explain clearly. Please. I can't understand. Explain in a simple manner please.
Vinay said:
1 decade ago
According to the problem,
First let us take length of the first train as "x"
So the length of the second train is half of the second train so it is half of x
So the total length is "(3/2)x"
and given that the two trains are travelling in opposite directions so that their relative speed = (48+42)km/hr.
now convert into m/s so it is 90*(5/18) =25 m/s.
from basic rule s = d /t;
25 m/s = ((3/2)x)/ 12 sec
by solving it we get x = 200m
and given that time required to pass platform is 45 sec
and length of platform = z
48 * (5/18) = (200+z) m/ 45 sec
by solving it we get finally 400 m
First let us take length of the first train as "x"
So the length of the second train is half of the second train so it is half of x
So the total length is "(3/2)x"
and given that the two trains are travelling in opposite directions so that their relative speed = (48+42)km/hr.
now convert into m/s so it is 90*(5/18) =25 m/s.
from basic rule s = d /t;
25 m/s = ((3/2)x)/ 12 sec
by solving it we get x = 200m
and given that time required to pass platform is 45 sec
and length of platform = z
48 * (5/18) = (200+z) m/ 45 sec
by solving it we get finally 400 m
Priya said:
1 decade ago
I think answer for length of the platform is 200m.
(400+y) /45=48*5/18.
Solving this we get y=200m.
(400+y) /45=48*5/18.
Solving this we get y=200m.
Nakul gowda said:
1 decade ago
@Vineet:
You are wrong buddy,,..you have to add train's length as well.
So it'd be 400+200=600/45*18/5 = 48 kmph.
You are wrong buddy,,..you have to add train's length as well.
So it'd be 400+200=600/45*18/5 = 48 kmph.
Sowjanya said:
1 decade ago
Can anybody explain this problem clearly ?
Vineet said:
1 decade ago
The answer isn't correct. It should be 600m.
Proof: If you go by other way taking length of the platform as 400m and time as 45 seconds.
Then the speed of the train would come as: (400/45)*(18/5)=32kmph(which isn't true)
Proof: If you go by other way taking length of the platform as 400m and time as 45 seconds.
Then the speed of the train would come as: (400/45)*(18/5)=32kmph(which isn't true)
Prabu said:
1 decade ago
After found the length of the first train then it will come to know about the length of 2nd train because (x/2).
When we find the length of the platform. Why did we use the first train length?
When we find the length of the platform. Why did we use the first train length?
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