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.
Nisha said:
1 decade ago
Why 9/250?
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
Sumi said:
1 decade ago
and u r rite priyavel but its not the time but speed which is 100km/hr
Did u get that nisha?
Did u get that nisha?
Vel said:
1 decade ago
60+40=100 (relative speed) bcoz opposite direction know
and we have to convert km into m
=100*5/18
=250/9
and we have to convert km into m
=100*5/18
=250/9
Sreejith c said:
1 decade ago
I got it.
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
Kiran said:
1 decade ago
How 300 m distance covered??
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
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?
Vineet Nair said:
1 decade ago
I still don't understand as how we got 5/18?
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