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:
43 comments Page 3 of 5.
Akhil v said:
1 year ago
Thanks all for explaining the answer.
Akhil R said:
2 months ago
Formula:
Time = (L₁ + L₂) / (S₁ + S₂)
Given:
L₁ = 140 m.
L₂ = 160 m.
S₁ = 60 × 5/18 = 50/3 m/s.
S₂ = 40 × 5/18 = 100/9 m/s.
Substitute:
Time = (140 + 160)/(50/3 + 100/9).
Time = 300/(250/9).
Time = 300 × 9/250.
Time = 10.8 seconds.
Time = (L₁ + L₂) / (S₁ + S₂)
Given:
L₁ = 140 m.
L₂ = 160 m.
S₁ = 60 × 5/18 = 50/3 m/s.
S₂ = 40 × 5/18 = 100/9 m/s.
Substitute:
Time = (140 + 160)/(50/3 + 100/9).
Time = 300/(250/9).
Time = 300 × 9/250.
Time = 10.8 seconds.
Ankiita said:
1 decade ago
Because when we convert km/hr into m/sec we multiply by 1000 & divide by 3600 so 1000/3600 after cancellation gives 5/18.
Priyavel said:
2 decades 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:
2 decades 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:
2 decades 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:
2 decades ago
I got it.
SATHEESH said:
2 decades 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
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