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:
54 comments Page 6 of 6.
Sugi said:
2 decades ago
Hi friends how that 3900 came ?
Ambika said:
2 decades 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
Thanu said:
2 decades ago
I was little confused. How that 5 came?
(1)
Uday said:
2 decades 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.
(1)
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