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 7 of 8.
Akber said:
1 decade ago
Assume one train is moving with X speed than other is twice faster it means 2x
look normal speed =x
twice the above speed=2*x=2x
look normal speed =x
twice the above speed=2*x=2x
Vel said:
1 decade ago
Hi seema rules wise we have to add the distance, relative speed based on the direction of both trains (same:-, opposite:+).
Kumaran6248 said:
1 decade ago
Here I wanna know! how we suppose to have 2x as fast train. Can any one suggest me"""If one is moving twice as fast the other""". And what about this?
Seema said:
1 decade ago
If these two trains are moving in opposite direction then how can we add their distance.
IKram said:
1 decade ago
Hey Jelli...
1) if 2 things moves in same direction:
time they meet t=(x+y)/(u-v)
where x,y-distance of trains or smthng
u,v-speed's in mps.
2) if 2 things moves in opposite direction:
time they meet t=(x+y)/(u+v)
1) if 2 things moves in same direction:
time they meet t=(x+y)/(u-v)
where x,y-distance of trains or smthng
u,v-speed's in mps.
2) if 2 things moves in opposite direction:
time they meet t=(x+y)/(u+v)
Mini said:
1 decade ago
Hi @jelli, I think this is correct.
length of each train=100 m
let speed of one train=x km/h
other is moving twice as fast the other i.e=2*x km/h
speed=distance/time
(x+2x)*5/18=200/8
x=30m
they are asking the speed of faster train which is 2*x
here we land up with x=30
So 2*30=60m
length of each train=100 m
let speed of one train=x km/h
other is moving twice as fast the other i.e=2*x km/h
speed=distance/time
(x+2x)*5/18=200/8
x=30m
they are asking the speed of faster train which is 2*x
here we land up with x=30
So 2*30=60m
Nayana said:
1 decade ago
Hi Arun,
Here we are converting km/h to m/s
so 1km=1000 meters
1hr=3600 sec
1km/h=1000/3600 m/s
1000/3600=5/18 m/s
Here we are converting km/h to m/s
so 1km=1000 meters
1hr=3600 sec
1km/h=1000/3600 m/s
1000/3600=5/18 m/s
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.
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