Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 9)
9.
Two trains are moving in opposite directions @ 60 km/hr and 90 km/hr. Their lengths are 1.10 km and 0.9 km respectively. The time taken by the slower train to cross the faster train in seconds is:
Answer: Option
Explanation:
Relative speed = (60+ 90) km/hr
| = |  |
150 x | 5 |  m/sec |
| 18 |
| = | |
125 | m/sec. |
| 3 |
Distance covered = (1.10 + 0.9) km = 2 km = 2000 m.
| Required time = | |
2000 x | 3 | sec = 48 sec. |
| 125 |
Discussion:
107 comments Page 6 of 11.
Mamata said:
1 decade ago
@jyoti,pratik
Both trains are moving opposite in direction.
So time taken by faster train to cross slower train is same as slower train by faster train.
Consider for faster train:
It must consider its speed and length along with another trains length and speed.
So time taken is same for both.
Both trains are moving opposite in direction.
So time taken by faster train to cross slower train is same as slower train by faster train.
Consider for faster train:
It must consider its speed and length along with another trains length and speed.
So time taken is same for both.
Ram said:
1 decade ago
Please explain the step 150*5/18=3/125 how it will came ?
Raj said:
1 decade ago
150*5/18=3/125
In this 150km/sec is relative speed of both trains(which comes by summed up two trains speed) which is in km/sec.we want to convert it to m/sec.so we are multiplying with 5/18 i.e.
(1km=1000m
1hr=3600sec
m/sec=1000/3600=5/18.)
relative speed=60+90=150km/sec.
then converting km/sec to m/sec=150*5/18=125/3.
In this 150km/sec is relative speed of both trains(which comes by summed up two trains speed) which is in km/sec.we want to convert it to m/sec.so we are multiplying with 5/18 i.e.
(1km=1000m
1hr=3600sec
m/sec=1000/3600=5/18.)
relative speed=60+90=150km/sec.
then converting km/sec to m/sec=150*5/18=125/3.
Sarvepalli.rajasekhar said:
1 decade ago
Consider u r standing on a platform.
When someone asked you how far is the train from the platform ur answer value reduces as the train is the train is closer and closer.
When it is moving away which means in opposite direction the distance increases.
So when the same thing assumed between two trains when they are moving in opposite direction from you the distances of both trains increases and total distance of two trains from you will be t1+ t2.
Than same can be applied to the speed or time.
5/18 is calculated value for 1000 kms / 3600 seconds (km/hr) used to convert km/hr in meter per second and the reverse 18/5 for meter per second into km per hour.
When someone asked you how far is the train from the platform ur answer value reduces as the train is the train is closer and closer.
When it is moving away which means in opposite direction the distance increases.
So when the same thing assumed between two trains when they are moving in opposite direction from you the distances of both trains increases and total distance of two trains from you will be t1+ t2.
Than same can be applied to the speed or time.
5/18 is calculated value for 1000 kms / 3600 seconds (km/hr) used to convert km/hr in meter per second and the reverse 18/5 for meter per second into km per hour.
Nil said:
1 decade ago
Here is the simple way.
60+90 km/hr = 150 km/hr = 150*1000/3600 = 41.66 m/sec (trains relative speed in mtr/sec)
Distance covered = 1.10+0.9 km = 2 km = 2000 m
Time taken by slower/faster train is the same = 2000/41.66 (time = distance/speed)= 48
60+90 km/hr = 150 km/hr = 150*1000/3600 = 41.66 m/sec (trains relative speed in mtr/sec)
Distance covered = 1.10+0.9 km = 2 km = 2000 m
Time taken by slower/faster train is the same = 2000/41.66 (time = distance/speed)= 48
Vaideki said:
1 decade ago
HI Raj good job .its an easy way to find the answer.Same direction means (x+y)/(u-v) if it opposite means (x+Y)/(u+v)
Sumit said:
1 decade ago
Length of the two trains=2km (the units I have taken is all in kms).
Relative speed is 150km/hr (this too in kms).
S=Length/Time=>time=length/speed.
Time=2/150=1/75 of a second i.e., 1/75*60 (converted into minutes) =4/5.
4/5*60 (into seconds) =48 sec.
Relative speed is 150km/hr (this too in kms).
S=Length/Time=>time=length/speed.
Time=2/150=1/75 of a second i.e., 1/75*60 (converted into minutes) =4/5.
4/5*60 (into seconds) =48 sec.
Gowtham said:
1 decade ago
How can add 1.10+.9 the train moves opposite direction so subract only pls clear my doubt
Sekhar said:
1 decade ago
Hi, I have a doubt
60+90= 150KM/hr i,e speed
distance covered is 1.10+0.9=2.0 km
Then you want time T=D/S = 2/150=1/75 in km/hr
You want to change in Mts 1/75*5/18 here iam not getting 48 sec.
60+90= 150KM/hr i,e speed
distance covered is 1.10+0.9=2.0 km
Then you want time T=D/S = 2/150=1/75 in km/hr
You want to change in Mts 1/75*5/18 here iam not getting 48 sec.
Vijay said:
1 decade ago
Why we want to multiply it by 3/125 instead of multiplying by 125/3?
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