Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 23)
23.
Two trains are running in opposite directions with the same speed. If the length of each train is 120 metres and they cross each other in 12 seconds, then the speed of each train (in km/hr) is:
Answer: Option
Explanation:
Let the speed of each train be x m/sec.
Then, relative speed of the two trains = 2x m/sec.
| So, 2x = | (120 + 120) |
| 12 |
2x = 20
x = 10.
 Speed of each train = 10 m/sec = |
 |
10 x | 18 |  |
km/hr = 36 km/hr. |
| 5 |
Discussion:
38 comments Page 2 of 4.
Keerthi said:
4 years ago
Let the speed of a single train be x m/sec.
length= 120m.
Time to cross each other= 12 sec.
There is a formula like,
a+b/u+v = time to cross each other,
(i.e) 120+120/2x = 12,
240/2x = 12,
X = 40.
= 40 * (18/5)hkm/hr,
= 144.
The Speed of each train is,
= 144/2.
= 72.
length= 120m.
Time to cross each other= 12 sec.
There is a formula like,
a+b/u+v = time to cross each other,
(i.e) 120+120/2x = 12,
240/2x = 12,
X = 40.
= 40 * (18/5)hkm/hr,
= 144.
The Speed of each train is,
= 144/2.
= 72.
(1)
Koli Jyoti said:
9 years ago
Let the speed of a singe train be x m/sec.
length= 120m.
time= 12 sec,
speed = length/time.
= 120/12.
= 10 m/s.
According to given question, they want speed in km/hr so we will convert it by formula (a*18/5)km/hr.
In our case a is 10m/s.
So
speed=(10*18/5)km/hr,
=36 km/hr.
length= 120m.
time= 12 sec,
speed = length/time.
= 120/12.
= 10 m/s.
According to given question, they want speed in km/hr so we will convert it by formula (a*18/5)km/hr.
In our case a is 10m/s.
So
speed=(10*18/5)km/hr,
=36 km/hr.
Swathi said:
10 years ago
Two vessels contains milk and water in the ratio 3:2 and 7:3 find the ratio in which the ratio contents of two vessels have to be mixed to get a mixture in which the ratio of the milk and water is 2:1?
Please solve this problem.
Please solve this problem.
Priyanka said:
10 years ago
Why are we ignoring the relative speed?
Rawoof said:
10 years ago
If you assume that you are sitting on one train:
When crossing another train, distance to move to the end of opp train = 120meters,
distance to move so the end of your trains reaches other trains tail is 120meters
Total distance = 120 + 120 = 240 metres.
Time taken = 12sec.
Relative speed = v + v = 2v.
2v = 240/12 = 20,
=> v= 10metres/sec.
v km/hr = 10 * (1/1000)/(1/3600) = 3600 * 10/1000 = 36km/hr.
When crossing another train, distance to move to the end of opp train = 120meters,
distance to move so the end of your trains reaches other trains tail is 120meters
Total distance = 120 + 120 = 240 metres.
Time taken = 12sec.
Relative speed = v + v = 2v.
2v = 240/12 = 20,
=> v= 10metres/sec.
v km/hr = 10 * (1/1000)/(1/3600) = 3600 * 10/1000 = 36km/hr.
Lambrud sachin said:
1 decade ago
Distance = 120 m,
Time = 12 sec, s = ?
So, T = D/S,
=> 12 = 120/s.
s = 120/12,
s = 10m/sec.
Then,
s = 10 * 18/5.
s = 36km/hr.
Time = 12 sec, s = ?
So, T = D/S,
=> 12 = 120/s.
s = 120/12,
s = 10m/sec.
Then,
s = 10 * 18/5.
s = 36km/hr.
Prashanth said:
1 decade ago
Why can't we consider as x kmph?
Shafiq said:
1 decade ago
Why the relative speed of the two trains is taken as 2x?
Rishi said:
1 decade ago
(120*18/5) = 432.
The length of train = Speed * Time.
120m = ? * 12 sec.
120/12 = 10 m/s.
So, 10*18/5 => 36 km/hr = Speed.
The length of train = Speed * Time.
120m = ? * 12 sec.
120/12 = 10 m/s.
So, 10*18/5 => 36 km/hr = Speed.
Souvanik said:
1 decade ago
Question is speed of each train?
Length of each train is 120 m and speed is also same.
So Speed = Distance/Time.
= 120/12 m/s.
= 10 m/s.
= 10*18/5 km/hr.
= 36 km/hr [1 m/s = 18/5 km/hr].
Answer will be 36 km/hr.
Length of each train is 120 m and speed is also same.
So Speed = Distance/Time.
= 120/12 m/s.
= 10 m/s.
= 10*18/5 km/hr.
= 36 km/hr [1 m/s = 18/5 km/hr].
Answer will be 36 km/hr.
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