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 2 of 11.
Adm said:
10 years ago
You have to add the lengths when you consider crossing each other and add speeds. For more understanding consider two trains moving at different speed and plot a graph for each sec as how much they cross each other and you will discover why the formula is:
Time for crossing = (Sum of length of two train)/(Sum of speed of two trains).
Time for crossing = (Sum of length of two train)/(Sum of speed of two trains).
(1)
Crack said:
6 years ago
I know why 5/18 is calculate. But in this particular math they didn't mention anything related to meter. Only answer is given in second, so we should only convert hr to seconds right? why we converted the km also? train length and speed both are in km, also in answer there's no km unit, only second. So please explain this part.
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.
Raj said:
1 decade ago
Use simple formula :
1)if 2 things acts in same direction( may be 2 trains or train&jogger)
time they meet t=(x+y)/(u-v)
where x,y-distance of trains or something
u,v-speed's in mps.
2)if 2 things acts in opposite direction:
time they meet t=(x+y)/(u+v)
1)if 2 things acts in same direction( may be 2 trains or train&jogger)
time they meet t=(x+y)/(u-v)
where x,y-distance of trains or something
u,v-speed's in mps.
2)if 2 things acts in opposite direction:
time they meet t=(x+y)/(u+v)
Subhransu said:
1 decade ago
Friend take a live example to make it understand when your going towards your home on the left side of the road and one of your friend returning from your home on your right side of the same road.
Definitely you will cross each other like this 2 train traveling in opposite direction they can cross each other.
Definitely you will cross each other like this 2 train traveling in opposite direction they can cross each other.
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.
Arun said:
1 decade ago
@jyoti :90>60 so train wit speed 60 s d slower train.. V need not calculate d speed of d faster train.. It can be done using d formula a+b/u+v... Where a is d distance trav by faster train and b s dat of slower..u and v r d speeds of faster and slower trains
Shweta said:
1 decade ago
It is the formula for,
The time taken by the trains to cross each other.
It is not as, faster cross the slower or slower cross the faster.
So we use this formula here also.
Answer in 2 step.
1. a+b/u+v : as both train in opposite direction
2. Answer*3600 : to convert it into sec.
The time taken by the trains to cross each other.
It is not as, faster cross the slower or slower cross the faster.
So we use this formula here also.
Answer in 2 step.
1. a+b/u+v : as both train in opposite direction
2. Answer*3600 : to convert it into sec.
Sateesh Vudum said:
1 decade ago
For every problem like this you should find relative speed to get solution.
Need of relative speed: we can desire the solution without forming the relation between two quantities either speed or time.
Time = (L1+L2)/(relative speed);
L1-Length of train-1.
L2-Length of train-2.
Need of relative speed: we can desire the solution without forming the relation between two quantities either speed or time.
Time = (L1+L2)/(relative speed);
L1-Length of train-1.
L2-Length of train-2.
Srividya said:
1 decade ago
Generally a+b\u-v formula is used to calculate the time taken by faster train to cross the slower train but in the question it is given that slower train to cross the faster train in this condition also we can use the same formula to find the answer can anyone explain me please.
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