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 5 of 8.
Praveen Sharma said:
10 years ago
Here (100+100)/8 = 3x.
200/8 = 3x.
25 = 3x.
So x = 25/3 m/s it is speed of slow train.
We want speed of fast train, it is 2x where x = 25/2 m/s.
So speed of fast train = 2*25/3 m/s.
So 50/3 m/s.
And we convert in km/s using 18/5.
So (50*18)/(3*5) = 900/15 = 60 km/h.
200/8 = 3x.
25 = 3x.
So x = 25/3 m/s it is speed of slow train.
We want speed of fast train, it is 2x where x = 25/2 m/s.
So speed of fast train = 2*25/3 m/s.
So 50/3 m/s.
And we convert in km/s using 18/5.
So (50*18)/(3*5) = 900/15 = 60 km/h.
(1)
Praveen Sharma said:
10 years ago
How come 3?
Answer - If speed of slow train is x km/h.
In question the speed of fast train is twice to slow train.
So speed of fast train = 2*(Speed of slow train).
So speed of fast train = 2*(x) = 2x.
If trains are moving in opposite direction then we ADD the Speed. And trains are in same direction then we sub speed.
Here train in same direction so we add the speed of both train.
So x + 2x = 3x.
Answer - If speed of slow train is x km/h.
In question the speed of fast train is twice to slow train.
So speed of fast train = 2*(Speed of slow train).
So speed of fast train = 2*(x) = 2x.
If trains are moving in opposite direction then we ADD the Speed. And trains are in same direction then we sub speed.
Here train in same direction so we add the speed of both train.
So x + 2x = 3x.
Sam said:
9 years ago
@Aditiyabala.
Super explanation, Thank you.
Super explanation, Thank you.
Vijay arun said:
9 years ago
@Ikram.
Nice explanation.
Nice explanation.
Jai said:
9 years ago
If 1st train accelerated by 0.3 and 2nd 0.2 then how to solve it?
Qweg said:
9 years ago
In this, we are not considering the distance that is between them? Should it be considered too?
Navin said:
9 years ago
x = 25/3
So, speed of the faster train = 50/3 m/sec.
I can't understand these steps please help me.
So, speed of the faster train = 50/3 m/sec.
I can't understand these steps please help me.
Sonam said:
8 years ago
@Adityabala.
Nice explanation. Thanks.
Nice explanation. Thanks.
R.Rakesh KUmar said:
8 years ago
@Navin.
In question they have mentioned to calculate the speed of faster train i.e to calculate 2X
X=25/3 is the speed of the slower train and ( " If one is moving twice as fast the other" given in question).
2 * X = 2 * 25/3 => 50/3.
In question they have mentioned to calculate the speed of faster train i.e to calculate 2X
X=25/3 is the speed of the slower train and ( " If one is moving twice as fast the other" given in question).
2 * X = 2 * 25/3 => 50/3.
K.ratnababu said:
8 years ago
This is another way.
two trains opposite direction 100m+100m=200m.
200m to cover 8 seconds then,
(200m 8sec
? 3600sec
90000m that means 90k).
3600sec that mean 1 hour to cover 90000m that is 90k/h.
the train speed is 2:1.
total 3 parts.
3parts 90kilometers then,
2parts ?
60k.
two trains opposite direction 100m+100m=200m.
200m to cover 8 seconds then,
(200m 8sec
? 3600sec
90000m that means 90k).
3600sec that mean 1 hour to cover 90000m that is 90k/h.
the train speed is 2:1.
total 3 parts.
3parts 90kilometers then,
2parts ?
60k.
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