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 28 of 48.
Nandhini said:
9 years ago
The given speed is 5 km/hr. How it comes 18/5?
PREM KUMAR said:
9 years ago
What are the formulas used to find the time?
Eldhose said:
9 years ago
Time(t) = Distance(s)/Speed.
S = ut + .5at^2
v = u + at
2as = (v^2 - u^2)
Where, a = acceleration, v = final vel, u = ini.vel, s = dist, t = time.
In these train equation, v and a are taken as zero.
S = ut + .5at^2
v = u + at
2as = (v^2 - u^2)
Where, a = acceleration, v = final vel, u = ini.vel, s = dist, t = time.
In these train equation, v and a are taken as zero.
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.
Pabitra mohan das said:
9 years ago
Why it is divided by 18/5?
Rishabh Suthar said:
9 years ago
Same direction then we do subtract and opposite direction then we do addition. Why?
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.
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