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 3 of 6.
Naveen said:
6 years ago
X+800 = 78 * 5/18 * 60,
X+800 = 13*5/3 *60,
X+800 = 13*5*20,
X+800 = 65*20,
X+800 = 1300,
X = 1300-800,
X = 500.
X+800 = 13*5/3 *60,
X+800 = 13*5*20,
X+800 = 65*20,
X+800 = 1300,
X = 1300-800,
X = 500.
Rohan said:
6 years ago
Why need to convert 1 minute to 60 seconds?
Khushi said:
4 years ago
@All.
Please correct me, if my calculation is wrong.
If we convert 78 km/hr into m/s.
So,
78 * 5/18.
390/18.
21.6 m/s.
Now if we put these value.
x + 800/60=21.6,
x + 800= 60 * 21.6,
x+800= 1296,
x= 1296 - 800.
x= 496.
Anyone please clarify this and explain with the correct answer.
Please correct me, if my calculation is wrong.
If we convert 78 km/hr into m/s.
So,
78 * 5/18.
390/18.
21.6 m/s.
Now if we put these value.
x + 800/60=21.6,
x + 800= 60 * 21.6,
x+800= 1296,
x= 1296 - 800.
x= 496.
Anyone please clarify this and explain with the correct answer.
Somil kumar bhadula said:
3 years ago
3(800+x) = 1900
2400+3x = 1900
3x = 2400-1900,
3x = 500.
I understand the thing. But where the 3x goes?
Can somebody tell me?
2400+3x = 1900
3x = 2400-1900,
3x = 500.
I understand the thing. But where the 3x goes?
Can somebody tell me?
Agggy said:
3 months ago
Why we are adding the length of train and length of tunnel? Anyone please explain to me.
Rishika V said:
2 months ago
@Agggy.
we add the length of the the train and tunnel because the train is said to have crossed the tunnel if and only if its entire part including the the very last end of it leaves the tunnel.
so if the train has crossed the tunnel in 1min then it would have covered the entire length of the tunnel and a certain distance outside the tunnel (the distance covered by the train until the very last end of the train leaves the tunnel).
So,
that 'certain distance' = length of the train.
.A______x______.B.______800______.C.
where x is the length of the tunnel and the length of the train is 800 m.
the total distance covered by the train is x + 800.
DISTANCE = X+800 m
SPEED = 78 km/hr
TIME = 60sec.
convert speed from km/hr to m/s.
SPEED = 78x1000/60 x 60.
SPEED = 65m/s.
distance /speed = time.
X + 800/65 = 60,
X + 800 = 60x65/3,
X + 800 = 3900/3,
X + 800 = 1300,
X = 1300 - 800,
X = 500.
we add the length of the the train and tunnel because the train is said to have crossed the tunnel if and only if its entire part including the the very last end of it leaves the tunnel.
so if the train has crossed the tunnel in 1min then it would have covered the entire length of the tunnel and a certain distance outside the tunnel (the distance covered by the train until the very last end of the train leaves the tunnel).
So,
that 'certain distance' = length of the train.
.A______x______.B.______800______.C.
where x is the length of the tunnel and the length of the train is 800 m.
the total distance covered by the train is x + 800.
DISTANCE = X+800 m
SPEED = 78 km/hr
TIME = 60sec.
convert speed from km/hr to m/s.
SPEED = 78x1000/60 x 60.
SPEED = 65m/s.
distance /speed = time.
X + 800/65 = 60,
X + 800 = 60x65/3,
X + 800 = 3900/3,
X + 800 = 1300,
X = 1300 - 800,
X = 500.
Sumana said:
1 decade ago
Why we convert 78 meter into seconds?
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 ?
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