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:
249 comments Page 15 of 25.
Sivakumar.s said:
1 decade ago
Train 130 meters long. Travel 45 km/hr.
To convert m/s = 25/2.
So 2 second train will move 25 meter. So 30 second means.
2*15 = 30 second.
25*15 = 375.
So train travelling 375 meters to reduce the train meters.
375-130 = 245.
So the bridge meter is 245 meters.
To convert m/s = 25/2.
So 2 second train will move 25 meter. So 30 second means.
2*15 = 30 second.
25*15 = 375.
So train travelling 375 meters to reduce the train meters.
375-130 = 245.
So the bridge meter is 245 meters.
(1)
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)
Sohail Khan said:
1 decade ago
We know that:
Time = Distance/Speed.
Suppose length of the bridge is X mtr.
Length of the train is 130 mtr.
So total distance = 130+X.
30 = (130+X)/45*(5/18).
Then the value of X is 245 mtr.
Time = Distance/Speed.
Suppose length of the bridge is X mtr.
Length of the train is 130 mtr.
So total distance = 130+X.
30 = (130+X)/45*(5/18).
Then the value of X is 245 mtr.
(1)
Vishali said:
1 decade ago
Hi friends I did in a different way:
Let the length of train b = 130.
Let the length of bridge b = x.
Therefore distance = x+130.
Time = 30 sec.
S = 45 km/h = 45*5/18 = 25/2 m/s.
So, in this case distance = 375 m.
So, d = x+130 substituting the value of d (distance).
We get 375-130 = x.
x = 245m.
Let the length of train b = 130.
Let the length of bridge b = x.
Therefore distance = x+130.
Time = 30 sec.
S = 45 km/h = 45*5/18 = 25/2 m/s.
So, in this case distance = 375 m.
So, d = x+130 substituting the value of d (distance).
We get 375-130 = x.
x = 245m.
(1)
Varalakshmi saravanan said:
1 decade ago
Hi Friends it's very simple.
Length of the Train = 130 m.
Speed = 45 km/hr after converting into m/s we will get (45*5/18) => 25/2.
Time = 30 sec.
Length of bridge = x + length of train.
X+length of train = Speed of the train*time.
X+130 = 25/2*30.
X+130 = 375.
X = 375-130.
X = 245.
Length of the Train = 130 m.
Speed = 45 km/hr after converting into m/s we will get (45*5/18) => 25/2.
Time = 30 sec.
Length of bridge = x + length of train.
X+length of train = Speed of the train*time.
X+130 = 25/2*30.
X+130 = 375.
X = 375-130.
X = 245.
Jagabandhu patra said:
1 decade ago
(45000/3600*30)-130 = 245.
(1)
Safina M said:
1 decade ago
Hey Radha,
Cross multiply (139+x)/30=25/2 i.e,
2*(130+x)=30*25.
i.e., 260+2x=750.
2x=750-260.
2x=490.
x=490/2.
Hence, x=245.
Cross multiply (139+x)/30=25/2 i.e,
2*(130+x)=30*25.
i.e., 260+2x=750.
2x=750-260.
2x=490.
x=490/2.
Hence, x=245.
Radha said:
1 decade ago
Please explain method clearly how we will dot 750?
SK Lodhi said:
1 decade ago
130+B = 30 Sec.*45*5/18 m/s(time*speed).
130+B = 375 m.
Where B = length of the Bridge = 375 - 130 = 245 meters.
130+B = 375 m.
Where B = length of the Bridge = 375 - 130 = 245 meters.
Suren said:
1 decade ago
@Sai.
Your method is fantastic and very easy to understand. Great job! keep it up man. Thanks!
Your method is fantastic and very easy to understand. Great job! keep it up man. Thanks!
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