Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 3)
3.
The length of the bridge, which a train 130 metres long and travelling at 45 km/hr can cross in 30 seconds, is:
Answer: Option
Explanation:
| Speed = |  |
45 x | 5 |  m/sec |
= | |
25 | m/sec. |
| 18 | 2 |
Time = 30 sec.
Let the length of bridge be x metres.
| Then, | 130 + x | = | 25 |
| 30 | 2 |
2(130 + x) = 750
x = 245 m.
Video Explanation: https://youtu.be/M_d8WufJWKc
Discussion:
245 comments Page 2 of 25.
Naveen Kumawat said:
9 years ago
Speed of train = 45 km/hr.
Or (45*100) m/(1*60*60) sec = (25/2) m/sec.
#----130m------>|________x meter_____________|cross in 30sec.
Train bridge.
|<--------------------130m+x---------------->|.
//# is the tail of train from where the crossing of bridge is observed.
So the total distance from # to end of the bridge is (130m+x).
And from distance formula:
Distance/Time = Speed.
i.e (130+x)/30 = 25/2.
Solving we get 245 m.
Or (45*100) m/(1*60*60) sec = (25/2) m/sec.
#----130m------>|________x meter_____________|cross in 30sec.
Train bridge.
|<--------------------130m+x---------------->|.
//# is the tail of train from where the crossing of bridge is observed.
So the total distance from # to end of the bridge is (130m+x).
And from distance formula:
Distance/Time = Speed.
i.e (130+x)/30 = 25/2.
Solving we get 245 m.
Priyanka Priyadarshini Samal said:
5 years ago
We have to calculate speed.
Speed = 45*5/18=25/2 m/s.
Time is given t= 30 sec.
Let's find the length of the bridge,
Let the length of the bridge is X.
And whenever a train crosses the bridge then the total distance covered by the train is the length of the bridge +it's own length (train's length),
According to the motion's 1st law distance or displacement = speed *time.
X+130 =25/2*30.
2(X+130)=750.
2X+260= 750.
X= (750-260)/2= 245m.
Speed = 45*5/18=25/2 m/s.
Time is given t= 30 sec.
Let's find the length of the bridge,
Let the length of the bridge is X.
And whenever a train crosses the bridge then the total distance covered by the train is the length of the bridge +it's own length (train's length),
According to the motion's 1st law distance or displacement = speed *time.
X+130 =25/2*30.
2(X+130)=750.
2X+260= 750.
X= (750-260)/2= 245m.
(1)
Riyaz said:
1 decade ago
Hi !
Actually we don't know the length of the bridge so we have to assume 'x' as like length of the bridge.
The answer is in meters so we should have to convert 45 km/hr in meters. Because it is in km/hr that's why we are using 5/18.45*5/18 = 25/2.
Train travelling distance and time is 130m+x/30sec = 25/2.
After that we need to find 'x' that is 2 (130+x) = 750. If you solve this equation then you can get 'x' that's the answer.
Actually we don't know the length of the bridge so we have to assume 'x' as like length of the bridge.
The answer is in meters so we should have to convert 45 km/hr in meters. Because it is in km/hr that's why we are using 5/18.45*5/18 = 25/2.
Train travelling distance and time is 130m+x/30sec = 25/2.
After that we need to find 'x' that is 2 (130+x) = 750. If you solve this equation then you can get 'x' that's the answer.
Raji said:
1 decade ago
Simple logic is, we know that speed = distance/time taken.
Distance can also be represented as length.
So, speed = length/time taken.
Therefore, length = speed*time taken.
Length= (45km/hr)/30.
Convert that km/hr into m/s. This is mandatory.
Then, length = (45*5/18) *30.
Length = 375m.
But an actual length can be calculated as,
Am denoting actual length as 'x'.
Therefore, x = length-train length.
= 375-130.
= 245m.
Distance can also be represented as length.
So, speed = length/time taken.
Therefore, length = speed*time taken.
Length= (45km/hr)/30.
Convert that km/hr into m/s. This is mandatory.
Then, length = (45*5/18) *30.
Length = 375m.
But an actual length can be calculated as,
Am denoting actual length as 'x'.
Therefore, x = length-train length.
= 375-130.
= 245m.
Kriti said:
1 decade ago
[][][][]```````````````[][][][]
```````````````
Train Bridge Train(and timer
(and timer stops here)
starts here)
<------------------------>
This is distance travelled by train in 30 sec (375m)
<--------------><-------->
Lenght of bridge Lenght of train (130m)
Lenght of bridge = distance travelled in 30 sec - lenght of train
Hence proved. : )
```````````````
Train Bridge Train(and timer
(and timer stops here)
starts here)
<------------------------>
This is distance travelled by train in 30 sec (375m)
<--------------><-------->
Lenght of bridge Lenght of train (130m)
Lenght of bridge = distance travelled in 30 sec - lenght of train
Hence proved. : )
Mukesh said:
1 decade ago
Given.....
train = 130m
speed = 45 km/hr or (75/6)m/s
time to cross bridge=30sec
Bcos the time is in sec thtat why we convert time in m/sec by multiplying and dividing 45 by 1000 and 3600 respectively
simple formula is distance=speed x time
=(75/6) x 30
=375 meters
now this distance is the distance which include train length also so less train length from this
=375-130
=245 meters
hence we get the ans
train = 130m
speed = 45 km/hr or (75/6)m/s
time to cross bridge=30sec
Bcos the time is in sec thtat why we convert time in m/sec by multiplying and dividing 45 by 1000 and 3600 respectively
simple formula is distance=speed x time
=(75/6) x 30
=375 meters
now this distance is the distance which include train length also so less train length from this
=375-130
=245 meters
hence we get the ans
Jitendra said:
1 decade ago
Can we try this way?
Length of train + Length of bridge = (Distance which train need to be cover in 30 sec).
(130 m + X)---(1)-X = Suppose length of bridge.
Speed of trains = 45 km/h speed given in km/h hence convert it in m/sec.
45*5/18 = 25/2 ----- (2).
From equation (1) and (2).
= 25/2 = (130+X)/30.
= 25*30 = 260+2X.
= 750-260 = 2X.
= 490/2 = X.
= 245 = X.
Hence length of bridge (X) will be 245 m.
Length of train + Length of bridge = (Distance which train need to be cover in 30 sec).
(130 m + X)---(1)-X = Suppose length of bridge.
Speed of trains = 45 km/h speed given in km/h hence convert it in m/sec.
45*5/18 = 25/2 ----- (2).
From equation (1) and (2).
= 25/2 = (130+X)/30.
= 25*30 = 260+2X.
= 750-260 = 2X.
= 490/2 = X.
= 245 = X.
Hence length of bridge (X) will be 245 m.
Ramkumar gadi said:
1 decade ago
Time taken by the train to cross object which is in motion in relative motion we have formulas:
T = (a+b)/(U+V) and T = (a+b)/(U-V).
Let be b = x.
So here we have U = Speed of train; a = Length of train = 130m.
V = Speed of object; B = Length of object.
V = 0; b = x; T = 30s.
S = 45 km/h = 45*5/18 = 25/2 m/s.
30 = (130+x)/(25/2+0).
= 30+25/2 = 130+x.
x = 245m.
T = (a+b)/(U+V) and T = (a+b)/(U-V).
Let be b = x.
So here we have U = Speed of train; a = Length of train = 130m.
V = Speed of object; B = Length of object.
V = 0; b = x; T = 30s.
S = 45 km/h = 45*5/18 = 25/2 m/s.
30 = (130+x)/(25/2+0).
= 30+25/2 = 130+x.
x = 245m.
(1)
Murali said:
1 decade ago
Hai! Janani while converting the distance it will come how means.
I) if you convert km/hr into m/sec then multiplies with "5/18".
Ii) if you convert m/sec into km/hr then multiplies with "18/5".
In this way, above problem the train speed is convert into the km/hr into m/sec. (because the answer is given in the form of meters).
Like this 5/18 will come.
I) if you convert km/hr into m/sec then multiplies with "5/18".
Ii) if you convert m/sec into km/hr then multiplies with "18/5".
In this way, above problem the train speed is convert into the km/hr into m/sec. (because the answer is given in the form of meters).
Like this 5/18 will come.
Mahesh said:
6 years ago
In order to convert a Km/hr to m/sec.
For 1km/hr.
1km=1000m.
1hr=3600sec.
Now 1000/3600=0.277m/sec.
for 45 km/hr.
45km= 45000.
1hr= 3600.
Now 45000/3600=12.5m/sec.
time taken is equal to 30 sec.
Let the length of the bridge be x meters.
Then 130+x/30= 12.5.
= 130+x = 12.5 * 30.
= x = 12.5 * 30-130.
Now x = 245m.
For 1km/hr.
1km=1000m.
1hr=3600sec.
Now 1000/3600=0.277m/sec.
for 45 km/hr.
45km= 45000.
1hr= 3600.
Now 45000/3600=12.5m/sec.
time taken is equal to 30 sec.
Let the length of the bridge be x meters.
Then 130+x/30= 12.5.
= 130+x = 12.5 * 30.
= x = 12.5 * 30-130.
Now x = 245m.
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