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:
478 comments Page 34 of 48.
Sophia said:
9 years ago
The best formula is:
Step1: distance = speed x time.
Then, speed = distance /time (125/10)m/sec.
=> (125/10)m/sec = (25/2)m/sec.
Step 2: convert m/sec to km/hr.
Note: 1000m - 1km.
3600sec - 60min - 1hr.
25m - 0.025km.
2sec - 0.0005hr.
Now (25/2)m/sec = (0.025/0.0005)km/hr. (0.025/0.0005)km/hr = 50km/hr.
Step1: distance = speed x time.
Then, speed = distance /time (125/10)m/sec.
=> (125/10)m/sec = (25/2)m/sec.
Step 2: convert m/sec to km/hr.
Note: 1000m - 1km.
3600sec - 60min - 1hr.
25m - 0.025km.
2sec - 0.0005hr.
Now (25/2)m/sec = (0.025/0.0005)km/hr. (0.025/0.0005)km/hr = 50km/hr.
Mounish said:
9 years ago
Distance = speed * time.
Speed = distance/time.
Speed = (x - 5)km/hr == (x - 5) * 5/18 m/sec.
Distance = 125 m.
Time = 10 sec.
(x - 5) * 5/18 = 125/10.
x - 5 = 125/10 * 18/5.
x - 5 = 45.
Speed = distance/time.
Speed = (x - 5)km/hr == (x - 5) * 5/18 m/sec.
Distance = 125 m.
Time = 10 sec.
(x - 5) * 5/18 = 125/10.
x - 5 = 125/10 * 18/5.
x - 5 = 45.
Rishabh Suthar said:
9 years ago
Same direction then we do subtract and opposite direction then we do addition. Why?
Pabitra mohan das said:
9 years ago
Why it is divided by 18/5?
Hasan Mahmud said:
9 years ago
Good job.
Laxman said:
9 years ago
Nice & excellent explanations, Thank you all.
SRIKANTH said:
9 years ago
Another method friends but bit lengthy.
D = S X T.
125 = (A - 25/18)10,
25 = (18A - 25)/9,
18A - 25 = 225,
18A = 250,
A = 250/18 X 18/5 = 50 KMPH.
D = S X T.
125 = (A - 25/18)10,
25 = (18A - 25)/9,
18A - 25 = 225,
18A = 250,
A = 250/18 X 18/5 = 50 KMPH.
Vignesh.Rv said:
9 years ago
Anyone tell me why its divided by 18/5?
Ramya said:
9 years ago
Please give the shortcut to solve the problem.
Ashish Dagar said:
9 years ago
Here, one thing I got to know is that, you all have missed a point and that was making a sense and hence considerable.
We can assume a stationary man or a pole of negligible length but this man was moving with a speed of 5km/hr and hence covered almost (10*(5*5/18)) meters in 10 seconds and so the length should be considered. Thus the answer is 55Km/hr instead of 50Km/hr.
We can assume a stationary man or a pole of negligible length but this man was moving with a speed of 5km/hr and hence covered almost (10*(5*5/18)) meters in 10 seconds and so the length should be considered. Thus the answer is 55Km/hr instead of 50Km/hr.
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