Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 17)
17.
A train 800 metres long is running at a speed of 78 km/hr. If it crosses a tunnel in 1 minute, then the length of the tunnel (in meters) is:
Answer: Option
Explanation:
| Speed = |  |
78 x | 5 |  |
m/sec | = | |
65 | |
m/sec. |
| 18 | 3 |
Time = 1 minute = 60 seconds.
Let the length of the tunnel be x metres.
| Then, | |
800 + x | |
= | 65 |
| 60 | 3 |
3(800 + x) = 3900
x = 500.
Discussion:
52 comments Page 1 of 6.
Uday said:
1 decade ago
I do not understand what is the meaning of crossing a tunnel you understand. I think it should mean the moment train head enters the tunnel till its TAIL comes out one can not consider the train is out of tunnel if its head just come out.
Thanu said:
1 decade ago
I was little confused. How that 5 came?
Ambika said:
1 decade ago
Hi Thanu,
It's so simple ,Frist we convert km/hr in to m/sec becase train length is given in metres, so multiple speed with 5/18; Then it becomes into 78*5/18=65/3m/sec
Now we can find the length of tunnels say it as "x"metres.
use formula
speed=(length of tunnel+length of train)/60;where 1 minute=60 sec
x+800/60=65/3;After calculation x=500
It's so simple ,Frist we convert km/hr in to m/sec becase train length is given in metres, so multiple speed with 5/18; Then it becomes into 78*5/18=65/3m/sec
Now we can find the length of tunnels say it as "x"metres.
use formula
speed=(length of tunnel+length of train)/60;where 1 minute=60 sec
x+800/60=65/3;After calculation x=500
Sugi said:
1 decade ago
Hi friends how that 3900 came ?
Narasimha said:
1 decade ago
Hi friends,
If tunnel is x metres
1 mint=60sec
800+x=78*(5/18)60
Solve this and get the ans
Length = Speed*Time
If tunnel is x metres
1 mint=60sec
800+x=78*(5/18)60
Solve this and get the ans
Length = Speed*Time
Gai3 said:
1 decade ago
Thank you ambika.
Deva said:
1 decade ago
I DIDNOT understand this example
A train 800 metres long is running at a speed of 78 km/hr. If it crosses a tunnel in 1 minute, then the length of the tunnel (in meters) is:
A train 800 metres long is running at a speed of 78 km/hr. If it crosses a tunnel in 1 minute, then the length of the tunnel (in meters) is:
Subham baksi said:
1 decade ago
Why (800+x) /60? Why divided 60 is not coming in my mind?
Ramesh said:
1 decade ago
Speed of train: 78kn/hr=78*(5/18)=21.67m/sec
Distance=800m
Time=60sec
d=s*t
800+x=21.67*60
x=1300.2-800=500
Distance=800m
Time=60sec
d=s*t
800+x=21.67*60
x=1300.2-800=500
Kannika said:
1 decade ago
Why we are adding train length to the tunnel length?
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