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:
476 comments Page 39 of 48.
K. Abhishek said:
6 years ago
@All.
Here, Train took 10 seconds to cross the person who is running at the speed of 5km/hr, then during this 10s the person might have travelled a certain distance, right? so train travelled (125m + distance covered by the man in 10s) in 10s then why the relative speed of train = 125/10?
How, will anyone explain it for me?
Here, Train took 10 seconds to cross the person who is running at the speed of 5km/hr, then during this 10s the person might have travelled a certain distance, right? so train travelled (125m + distance covered by the man in 10s) in 10s then why the relative speed of train = 125/10?
How, will anyone explain it for me?
Yugapooja said:
6 years ago
Thanks for the explanation @Rahul.
ABHISHEK said:
6 years ago
The speed of train with respect to ground=125/10=25/2 (m/sec).
Now to covert into km/hr:(25/2)*(3600/1000)=45 Km/hr.
Now there is a formula:
Velocity of train w.r.t. man(45 km/hr)=velocity of train w.r.t. ground(let it be x) - velocity of man w.r.t. ground(5km/hr).
So,
45 = x-5.
i.e. x = 50 Km/hr.
Now to covert into km/hr:(25/2)*(3600/1000)=45 Km/hr.
Now there is a formula:
Velocity of train w.r.t. man(45 km/hr)=velocity of train w.r.t. ground(let it be x) - velocity of man w.r.t. ground(5km/hr).
So,
45 = x-5.
i.e. x = 50 Km/hr.
Shashank shekhar said:
6 years ago
Train crossing a moving object without length in same direction:
Formula is :-
Time=length of train / ( speed of train-speed of object).
10 sec = 125 m/ ( x - 5*5/18).
So, x=125/9 m/sec = 125/9 * 18/5 km/h = 50 km/h.
Formula is :-
Time=length of train / ( speed of train-speed of object).
10 sec = 125 m/ ( x - 5*5/18).
So, x=125/9 m/sec = 125/9 * 18/5 km/h = 50 km/h.
(1)
Sai ganesh said:
6 years ago
as per my opinion The question is given in m/sec so the answer should be converted into 1 hr = 3600 sec and 1 km = 1000 m.
(3600/1000) m/sec as per given question.
125m and 10 sec,
(125/10)m/sec=45m/sec.
Here the man is moving in the same direction so we should subtract.
(x-5)=45.
x = 50km/hr.
(3600/1000) m/sec as per given question.
125m and 10 sec,
(125/10)m/sec=45m/sec.
Here the man is moving in the same direction so we should subtract.
(x-5)=45.
x = 50km/hr.
Mangaldeep Ghosh said:
6 years ago
Why ((a+b)/(u-v)) = t does not work?
Where a=length of the train (125 meters).
b= length of object( 0 meter),
u = speed of train ( let, x m/s),
t = time taken to cross the object,
v = speed of object (5 km/hr).
Where a=length of the train (125 meters).
b= length of object( 0 meter),
u = speed of train ( let, x m/s),
t = time taken to cross the object,
v = speed of object (5 km/hr).
Vishwa Telagadi said:
6 years ago
Man's speed=5 km/hr = 5 * 5/18 = (25/18)m/s.
The distance covered by man in 10 sec = (25/18)*10=(250/18)m,
Therefore distance covered by train for crossing the man=125+250/18=1250/9m,
Therefore speed=(1250/9)/10=125/9 m/s,
=(125/9)*3600/1000,
=(125/9)*(18/5)=50 km/hr.
The distance covered by man in 10 sec = (25/18)*10=(250/18)m,
Therefore distance covered by train for crossing the man=125+250/18=1250/9m,
Therefore speed=(1250/9)/10=125/9 m/s,
=(125/9)*3600/1000,
=(125/9)*(18/5)=50 km/hr.
Arun said:
6 years ago
How we say 45 km/hr is a relative speed?
Omsingh more said:
6 years ago
They should mention "relative speed" in the question. Why it is not so? It confuses the examiner!
Suresh said:
6 years ago
125m
5km/hr
10sec
Speed=distance/time.
Therefore S=km/hr(it's convert to m/sec)
S=1000m/3600sec
S=5/18.
Therefore S=D/T
D=125m
T=10sec
S=125/10
S=12.5, S=5/18.
Therefore 12.5=5/18=S(cross multiplication)
S = 12.5 * 18/5.
S = 225/5,
S = 45km/hr.
Remaining train running speed is added.
Therefore S = 45 + 5.
= 50km/hr.
5km/hr
10sec
Speed=distance/time.
Therefore S=km/hr(it's convert to m/sec)
S=1000m/3600sec
S=5/18.
Therefore S=D/T
D=125m
T=10sec
S=125/10
S=12.5, S=5/18.
Therefore 12.5=5/18=S(cross multiplication)
S = 12.5 * 18/5.
S = 225/5,
S = 45km/hr.
Remaining train running speed is added.
Therefore S = 45 + 5.
= 50km/hr.
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