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 45 of 48.
Sanya said:
1 decade ago
relative speed when two movable things whose speeds x,y are moving in same direction is =X-Y,
relative speed when two movable things whose speeds x,y are moving in OPPOSITE direction is =X+Y
Its an standard formula
relative speed when two movable things whose speeds x,y are moving in OPPOSITE direction is =X+Y
Its an standard formula
CHAKIT said:
1 decade ago
x - 5 = 45
x= 45+5
x = 50 km/hr.
x= 45+5
x = 50 km/hr.
Sathish said:
1 decade ago
(x-5) is not a standard formula x is taken as speed of train and 5 is man's speed, to calculate train's speed from relative speed we subtract (x-5).
San said:
1 decade ago
I cant understand relative speed formula ie) x-5 is this standard formula ?
Anitha Alavala said:
1 decade ago
See the answer for 18/5 is how?
1 km=1000m & 1hr=3600sec by this we get 1km/1hr = 5/18 m/sec.But
the answer must be in km/hr....But 5/18 is in m/sec. we have to convert it to km/hr.
1 km = 1000m => m = 1 km/1000 hr/3600)
= (1km/1000)*(3600/1hr)
= 3600km/1000hr => 18/5 km/hr
friends...its a perfect answer...have a look.
1 km=1000m & 1hr=3600sec by this we get 1km/1hr = 5/18 m/sec.But
the answer must be in km/hr....But 5/18 is in m/sec. we have to convert it to km/hr.
1 km = 1000m => m = 1 km/1000 hr/3600)
= (1km/1000)*(3600/1hr)
= 3600km/1000hr => 18/5 km/hr
friends...its a perfect answer...have a look.
Anitha said:
1 decade ago
Why 18/5 please tell me?
Atique said:
1 decade ago
Nice Explanation Guys. Thanks a Lot.
K.C.Yogannal said:
1 decade ago
@Vijayagopal.
As speed =length/time they have done 125/10. Where 125 is the length and 10 is the time. Hope you understood.
As speed =length/time they have done 125/10. Where 125 is the length and 10 is the time. Hope you understood.
Nitesh Nandwana said:
1 decade ago
Hai Rahul, well explanation about relative speed and same and opposite directions. Good job keep it up.
Manoj Chauhan said:
1 decade ago
125/10 = 12.5
3600/1000 = 36/10 (you should delete the last two zeros)
36/10 = 3.6
x = 12.5 * 3.6
So that x = 45 per hour right (this is relative speed of train)
x = 45 (you add 5 km per hour for train speed because 45 is relative speed of train).
Therefore x = 50 (the required answer).
3600/1000 = 36/10 (you should delete the last two zeros)
36/10 = 3.6
x = 12.5 * 3.6
So that x = 45 per hour right (this is relative speed of train)
x = 45 (you add 5 km per hour for train speed because 45 is relative speed of train).
Therefore x = 50 (the required answer).
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