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 2 of 8.
Riqual said:
5 years ago
@Nutan.
How come 18/3?
How come 18/3?
Deepa sri said:
5 years ago
Let;
Speed of slower train (u) = X m/sec.
Speed of faster train(v) = 2X m/sec.
Because the second train is twice as faster the first train.
Each train is 100 m long So
a=100,
b=100.
Two trains are running in the opposite direction, So (u+v).
u+v=x+2x
=3x.
Time = 8sec
a+b/u+v = time
100+100/3x = 8;
200/3x = 8;
X = 25/3 m/sec;
X = 25/3*18/5 km/hr,
= 30 km/hr.
Speed of faster train = 2x.
=2*30.
=60km/hr.
Speed of slower train (u) = X m/sec.
Speed of faster train(v) = 2X m/sec.
Because the second train is twice as faster the first train.
Each train is 100 m long So
a=100,
b=100.
Two trains are running in the opposite direction, So (u+v).
u+v=x+2x
=3x.
Time = 8sec
a+b/u+v = time
100+100/3x = 8;
200/3x = 8;
X = 25/3 m/sec;
X = 25/3*18/5 km/hr,
= 30 km/hr.
Speed of faster train = 2x.
=2*30.
=60km/hr.
(4)
Dewansh said:
6 years ago
Why the relative speed is the sum of individual speeds rather than the difference?
Arifur Rahman said:
6 years ago
Let,
The speed of slower train be x m/sec.
The speed of faster train be 2x m/s.
Now,
(x+2x)÷2(two trains) = 100/8.
or,x=25/3.
The Speed of faster train = 2x = 2 * 25/3 = 50/3 m/sec * 18/5 = 60km/hr.
The speed of slower train be x m/sec.
The speed of faster train be 2x m/s.
Now,
(x+2x)÷2(two trains) = 100/8.
or,x=25/3.
The Speed of faster train = 2x = 2 * 25/3 = 50/3 m/sec * 18/5 = 60km/hr.
Manivel said:
6 years ago
@Punam.
Substitute the X value in faster train 2X, 2* (25/3) =50/3. M.
Substitute the X value in faster train 2X, 2* (25/3) =50/3. M.
Punam said:
6 years ago
How come 50/3?
Sowdi said:
7 years ago
Thanks for your explanation @Sarang.
Sunil bhanovath said:
7 years ago
@Nutan.
Why 50/3 taken as speed of the train is 2x so that's why we should take.
Why 50/3 taken as speed of the train is 2x so that's why we should take.
Nutan said:
7 years ago
(50/3) * (18/3) = 60 how?
Ganesh said:
7 years ago
Consider one train x speed and another one is x one twice speed to the other train then x+2x-3x.
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