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 38 of 48.
Jeevitha said:
8 years ago
Somebody asking that why x-5 here. Note that the man running in the same direction. So we have to subtract. If it is opp we have to add. Because man beats train spd. So man power should be subtracted. Then only we can get an exact speed of the train.
Shreya Parmar said:
8 years ago
Using [a+b] / [u-v] = t.
a = size of train = 125
b = size of man = 0
u = speed of train = ?
v = speed of man = 5km/hr =5*5/18 = 25/18 m/s
t = time by which train crosses the man =10 sec
substitute the values in the formula we have,
[125-0]/[u- 25/18] = 10
further solving we get
250/18 =u; which is in m/s
now convert it into km/h by multiplying LHS with 18/5
we have u =50km/h
which is the right answer.
a = size of train = 125
b = size of man = 0
u = speed of train = ?
v = speed of man = 5km/hr =5*5/18 = 25/18 m/s
t = time by which train crosses the man =10 sec
substitute the values in the formula we have,
[125-0]/[u- 25/18] = 10
further solving we get
250/18 =u; which is in m/s
now convert it into km/h by multiplying LHS with 18/5
we have u =50km/h
which is the right answer.
Apple said:
8 years ago
What is 5/18? please explain.
Amar G J said:
8 years ago
It is the conversion of km/hr to m/s.
km/hr = 1000/3600 = 5/18m/s.
km/hr = 1000/3600 = 5/18m/s.
Angel said:
8 years ago
@Bala.
Speed=(Distance/Time).
Here distance is the length of the train which is 125 m and the time is 10 s
speed=125/10.
Speed=(Distance/Time).
Here distance is the length of the train which is 125 m and the time is 10 s
speed=125/10.
Ashis said:
8 years ago
5 km/h convert into m/s =5*1000/3600 or 5*5/18 =1.38,
Distance traveled by man in 10 sec = 1.38*10=13.8,
Total distance traveling by train =125m +13.8m =138.8,
Final speed of train in 10 sec = 13.88m/s=49.968km/h.
Some error because of 1.38 is approximate.
Distance traveled by man in 10 sec = 1.38*10=13.8,
Total distance traveling by train =125m +13.8m =138.8,
Final speed of train in 10 sec = 13.88m/s=49.968km/h.
Some error because of 1.38 is approximate.
Chithra said:
8 years ago
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.
Similarly, the reciprocal of m/sec is used to calculate km/hr.
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.
Similarly, the reciprocal of m/sec is used to calculate km/hr.
Priya said:
8 years ago
As both the man and train are moving in the same direction than why the relative is subtracted by 5 i.e, x-5 it should be x+5?
Yuvraj said:
8 years ago
Speed=Distance(length of train)/Time;
s=125/10;
But s is (speed of train and man together i.e man's speed is 5km/hr so convert 5*(5/18)& train and man going in same direction that's why -X (let the speed of train)
(X*(5/18))-(5*(5/18))=125/10,
x-5=45,
x=50.
s=125/10;
But s is (speed of train and man together i.e man's speed is 5km/hr so convert 5*(5/18)& train and man going in same direction that's why -X (let the speed of train)
(X*(5/18))-(5*(5/18))=125/10,
x-5=45,
x=50.
Mustufa said:
8 years ago
As we find train speed pass near to man is 45 km/hr and man also running at speed of 5 km/hr so we add train speed with man speed so we get the exact speed of train.
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