Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 13)
13.
Two trains, each 100 m long, moving in opposite directions, cross each other in 8 seconds. If one is moving twice as fast the other, then the speed of the faster train is:
Answer: Option
Explanation:
Let the speed of the slower train be x m/sec.
Then, speed of the faster train = 2x m/sec.
Relative speed = (x + 2x) m/sec = 3x m/sec.
 |
(100 + 100) | = 3x |
| 8 |
24x = 200
| x = |
25 | . |
| 3 |
| So, speed of the faster train = | 50 | m/sec |
| 3 |
| = |  |
50 | x | 18 |  km/hr |
| 3 | 5 |
= 60 km/hr.
Discussion:
74 comments Page 6 of 8.
Arun said:
1 decade ago
What is 5/18? How the value will come?
Jelli said:
1 decade ago
It's very simple i think
WKT t=(a+b)/(u-v)
here
t=8s,a=b=100m,u=x,v=2x(twice fast of other)
8=(100+100)/(x+2x)*5/18
x=30m
then in the problem they asked length of the faster train is 2x=60m.
WKT t=(a+b)/(u-v)
here
t=8s,a=b=100m,u=x,v=2x(twice fast of other)
8=(100+100)/(x+2x)*5/18
x=30m
then in the problem they asked length of the faster train is 2x=60m.
Jyoti said:
1 decade ago
Dear ravi this is speed of first train +speed of second train=relative speed of both trains moving opposite.
Manoj said:
1 decade ago
Please guide me step by step in calculation.
Nagashree said:
1 decade ago
In the question they have mentioned that we have to find the train which is twice as fast the other hence we have to multipy (25 x 2)/3 = 50/3.
Jagdish said:
2 decades ago
I don't understand how is speed of the faster train = 50/3 m/sec.
Vaibhav said:
1 decade ago
Here there is no need of finding relative speed right? then why we find relative speed?
Ravi said:
2 decades ago
What is (100+100)/8=3x?
Anshul Saraf said:
1 decade ago
Here both trains will not travel the same distance of 100 m. However the sum of distance travelled by both trains will be 200.
Priyesh Jain said:
1 decade ago
"D = ST".
Total distance = 100+100 = 200 m.
Relative speed = s+2s = 3s.
T= 8 sec.
Putting these values.
200 = 3s*8.
S = 200/8*3.
S = 25/3 m/s.
Now be need to calculate speed in terms of km/h.
25/3*18/5 = 30 km/h.
Speed of slower train now speed of faster train is 60 km/h that is just double.
Total distance = 100+100 = 200 m.
Relative speed = s+2s = 3s.
T= 8 sec.
Putting these values.
200 = 3s*8.
S = 200/8*3.
S = 25/3 m/s.
Now be need to calculate speed in terms of km/h.
25/3*18/5 = 30 km/h.
Speed of slower train now speed of faster train is 60 km/h that is just double.
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