Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 14)
14.
Two trains 140 m and 160 m long run at the speed of 60 km/hr and 40 km/hr respectively in opposite directions on parallel tracks. The time (in seconds) which they take to cross each other, is:
Answer: Option
Explanation:
| Relative speed = (60 + 40) km/hr = |  |
100 x | 5 |  m/sec |
= | |
250 | m/sec. |
| 18 | 9 |
Distance covered in crossing each other = (140 + 160) m = 300 m.
| Required time = | |
300 x | 9 | sec |
= | 54 | sec = 10.8 sec. |
| 250 | 5 |
Discussion:
42 comments Page 1 of 5.
Priyavel said:
1 decade ago
Hello friend
1)speed=distance/time
2)here time should be calculate so time=distance/ speed
3) distance=300 (opposite direction so we add it)
4)time= 100 (opposite direction so we add it) then we want to convert km into m,hour into sec so we multiply 5/18 so we get it 100*5/18=250/9
5)time=300(distance)/(250/9)=300*9/250.
i think u get clear id
1)speed=distance/time
2)here time should be calculate so time=distance/ speed
3) distance=300 (opposite direction so we add it)
4)time= 100 (opposite direction so we add it) then we want to convert km into m,hour into sec so we multiply 5/18 so we get it 100*5/18=250/9
5)time=300(distance)/(250/9)=300*9/250.
i think u get clear id
SATHEESH said:
1 decade ago
Speed=distance/time....
So time=distance/speed...
We know that distance=300 and speed=250/9....
So by substituting the speed value 250/9 along with distance value in the above formula we get the time required.
IN such CASE THE DINOMINATOR 250/9(SPEED CAN BE RECIPROCATED TO THE NUMERATOR FOR SIMPLICATION SUCH THAT VALUE BECOMES 9/250 IN NUMERATOR
So time=distance/speed...
We know that distance=300 and speed=250/9....
So by substituting the speed value 250/9 along with distance value in the above formula we get the time required.
IN such CASE THE DINOMINATOR 250/9(SPEED CAN BE RECIPROCATED TO THE NUMERATOR FOR SIMPLICATION SUCH THAT VALUE BECOMES 9/250 IN NUMERATOR
Praveen said:
10 years ago
Let time is x sec. According to question:
Speed = Length/Time.
Both are in opposite so we add the speed if in same direction then sub speed.
So speed = 60+40 = 100 km/h.
We convert it in m/s by multiply 5/18.
So speed = 250/9 m/s.
Length = 140 m + 160 m = 300 m.
And time = x sec.
So 250/9 = 300/x.
So x = (300*9)/250.
And time = 10.8 sec.
Speed = Length/Time.
Both are in opposite so we add the speed if in same direction then sub speed.
So speed = 60+40 = 100 km/h.
We convert it in m/s by multiply 5/18.
So speed = 250/9 m/s.
Length = 140 m + 160 m = 300 m.
And time = x sec.
So 250/9 = 300/x.
So x = (300*9)/250.
And time = 10.8 sec.
Gourish said:
1 decade ago
I have one confusion regarding the length as the trains are moving opposite direction the length should be the longest train time as the time taken to cross will be dependent on direction.
Had it been same direction the trains length should be added.
A ---------
--------------- B
Anyone please?
Had it been same direction the trains length should be added.
A ---------
--------------- B
Anyone please?
Praveen Sharma said:
10 years ago
Convert km/h in m/sec.
In first we have 1 km = 1000 m.
In second we have 1 hour = 60 min.
And 1 min = 60 sec.
So total sec in 1 hrs = 60 x 60 = 3600 sec.
So 1000 m/3600 sec = 10/36 [cut 2 zero].
And finally divided by 2 both number.
So 5/18 m/s.
I hope it is useful for non-maths students.
In first we have 1 km = 1000 m.
In second we have 1 hour = 60 min.
And 1 min = 60 sec.
So total sec in 1 hrs = 60 x 60 = 3600 sec.
So 1000 m/3600 sec = 10/36 [cut 2 zero].
And finally divided by 2 both number.
So 5/18 m/s.
I hope it is useful for non-maths students.
P.hari krishna said:
1 decade ago
Hi friends you will get answer in very simple manner like this we will use ((a+b) / (u+v)).
Length of trains=140+160=300.
Speeds in opposite direction=60+40=100km/hr= (100*5/18) m/h.
So,
T= ( (300/100) *18/5) =54/5=10.8
Length of trains=140+160=300.
Speeds in opposite direction=60+40=100km/hr= (100*5/18) m/h.
So,
T= ( (300/100) *18/5) =54/5=10.8
Sourabh Sonwane said:
5 years ago
a = 140
b = 160
u = 60km/h
v = 40km/h
u+v = 60 + 40 = 100km/h.
Now convert km/h into m/s then,
100*5/18=27.77.
As we know the formula.
a+b/u + v.
Putting all values in formulas.
140 + 160/27.77 = 10.8.
b = 160
u = 60km/h
v = 40km/h
u+v = 60 + 40 = 100km/h.
Now convert km/h into m/s then,
100*5/18=27.77.
As we know the formula.
a+b/u + v.
Putting all values in formulas.
140 + 160/27.77 = 10.8.
(6)
Indraneel Mal said:
2 years ago
72kmph = 20m/sec.
In 26 seconds, the distance covered = 20 * 26 = 520m.
As the length of the platform is 250m.
Therefore the length of the train = 520 - 250 = 270m.
In 26 seconds, the distance covered = 20 * 26 = 520m.
As the length of the platform is 250m.
Therefore the length of the train = 520 - 250 = 270m.
(5)
Vinayak said:
1 decade ago
A _______|
|_______________ B
Hence, Length = A+B.
As they start crossing each other when engine meet and end crossing when their tail meets.
Rahul kumat said:
1 decade ago
How relative speed added? As in question number 9 also when trains moving in opposite direction relative is added in both case relative speed is added? How?
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