Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 2)
2.
A train 125 m long passes a man, running at 5 km/hr in the same direction in which the train is going, in 10 seconds. The speed of the train is:
Answer: Option
Explanation:
| Speed of the train relative to man = |  |
125 |  m/sec |
| 10 |
| = | |
25 | m/sec. |
| 2 |
| = | |
25 | x | 18 | km/hr |
| 2 | 5 |
= 45 km/hr.
Let the speed of the train be x km/hr. Then, relative speed = (x - 5) km/hr.
x - 5 = 45 
x = 50 km/hr.
Discussion:
475 comments Page 26 of 48.
Rishi said:
1 decade ago
Answer must be 55, Because train has to cover 125m+distance covered by man in 10 sec which is 5*10/3600.
Vishal patel said:
1 decade ago
L = Length of a train.
S1 = Speed of train.
S2 = Speed of man.
T = Time taken by train.
*************** Here is simple formula *********************
T = L/(S1 - S2) * (18/5).
************************************************
10 = 125/(S1 - 5) * (18/5).
=> (S1 - 5) = (125/10)*18/5.
=> (S1 - 5) = (25/2)*18/5.
=> (S1 - 5) = 45.
=> S1 = 45 + 5.
Ans : S1(train's speed) = 50 km/h.
S1 = Speed of train.
S2 = Speed of man.
T = Time taken by train.
*************** Here is simple formula *********************
T = L/(S1 - S2) * (18/5).
************************************************
10 = 125/(S1 - 5) * (18/5).
=> (S1 - 5) = (125/10)*18/5.
=> (S1 - 5) = (25/2)*18/5.
=> (S1 - 5) = 45.
=> S1 = 45 + 5.
Ans : S1(train's speed) = 50 km/h.
Jasper said:
1 decade ago
How it is saying that relative speed of the train is 45?
Its only the speed of the train, can anyone tell me?
Its only the speed of the train, can anyone tell me?
Munna raj said:
1 decade ago
Let me explain about converting km/hr into m/s in detail.
1 km = 1000 meters.
1 hr = 3600 seconds.
1 km/hr = 1000/3600 m/s.
= 10/36 m/s.
= 5/18 m/s.
Therefore 1 km/hr = 5/18 m/sec.
1 km = 1000 meters.
1 hr = 3600 seconds.
1 km/hr = 1000/3600 m/s.
= 10/36 m/s.
= 5/18 m/s.
Therefore 1 km/hr = 5/18 m/sec.
Revathi said:
1 decade ago
Nice explanations are there but still I have a doubt. Can anyone tell me which speed has to subtract in relative motion?
Nanda said:
1 decade ago
Relative speed = (x-5) km/hr and x-5 = 45.
What is the inner meaning for that can any one say?
What is the inner meaning for that can any one say?
Nanda said:
1 decade ago
@ Revathi.
What ever the speed we got first 45 km/hr that is not train speed, that is relative speed because it will come by the intervention of the man speed.
Now we have to cal calculate train speed by follows.
Let the speed of the train be x km/hr.
Relative speed(45kms) = x-5(man speed).
Now x = relative speed(45kms) + 5(right side 5 will come to left side).
Finally x(speed of train) = 45+5 = 50.
What ever the speed we got first 45 km/hr that is not train speed, that is relative speed because it will come by the intervention of the man speed.
Now we have to cal calculate train speed by follows.
Let the speed of the train be x km/hr.
Relative speed(45kms) = x-5(man speed).
Now x = relative speed(45kms) + 5(right side 5 will come to left side).
Finally x(speed of train) = 45+5 = 50.
Gogul prasath said:
1 decade ago
Relative speed is difference between speed of train and speed of man.
x: Speed of train.
5: Speed of man.
Difference is (x-5) = 45.
45 is relative speed.
x: Speed of train.
5: Speed of man.
Difference is (x-5) = 45.
45 is relative speed.
Nish said:
1 decade ago
When we convert km/h to m/sec in that situation we multiple 5/18 and same opposition 18/5.
Jansi said:
1 decade ago
Could you explain how to calculate downstream in still water with example?
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