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 7 of 11.
Nitish said:
1 decade ago
Don't worry about it.
Use simple idea of relative speed and distance.
S = U*T.
Where S = Relative distance.
U = Relative Speed of train.
T = Time taken by train.
Note:
1. If one train is crossing bridge/platform then take relative distance as "sum of length of train and bridge/platform".
2. If both are in same direction then subtracts the speeds.
3. If both are in opposite direction then add the speeds.
4. If one Train is crossing "man" then his speed is "Zero".
Use simple idea of relative speed and distance.
S = U*T.
Where S = Relative distance.
U = Relative Speed of train.
T = Time taken by train.
Note:
1. If one train is crossing bridge/platform then take relative distance as "sum of length of train and bridge/platform".
2. If both are in same direction then subtracts the speeds.
3. If both are in opposite direction then add the speeds.
4. If one Train is crossing "man" then his speed is "Zero".
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.
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.
Maurya vinay lucknow said:
1 decade ago
T = D/S .
D = 2 KM = 2000M.
S = 150KM/HR = 150X5/18 = 125/3.
T = 2000/[125/3] = 2000X3/125 = 48 sec.
D = 2 KM = 2000M.
S = 150KM/HR = 150X5/18 = 125/3.
T = 2000/[125/3] = 2000X3/125 = 48 sec.
Vijay said:
1 decade ago
Why we want to multiply it by 3/125 instead of multiplying by 125/3?
Dharmender said:
1 decade ago
@Sekhar.
If Initially you are not convert distance and speed in meter and m/s then after getting time you multiply only by 3600 for getting 48 sec.
Because Unit of Time is Only hour or seconds.
As T=D/S
So unit of T=(Unit of distance)/(Unit of Speed)
So you get Unit of Time is Only hour or seconds
Time T=D/S = 2/150=1/75*3600=48 sec.
If Initially you are not convert distance and speed in meter and m/s then after getting time you multiply only by 3600 for getting 48 sec.
Because Unit of Time is Only hour or seconds.
As T=D/S
So unit of T=(Unit of distance)/(Unit of Speed)
So you get Unit of Time is Only hour or seconds
Time T=D/S = 2/150=1/75*3600=48 sec.
(1)
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.
Gowtham said:
1 decade ago
How can add 1.10+.9 the train moves opposite direction so subract only pls clear my doubt
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.
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)
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