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 36 of 48.
Rachit said:
8 years ago
RELATIVE SPEED OF TRAIN WITH RESPECT TO MAN RUNNING= (x-5)km/hr.
TIME=DISTANCE/RELATIVE SPEED.
Therefore we know that- to convert km/hr to m/s we have to use,
(x-5) * 5/18)m/sec.
TIME=DISTANCE/RELATIVE SPEED
10=125/(x-5)*5/18.
10=TIME,125=DISTANCE,(x-5)*5/18=RELATIVE SPEED
CALCULATION-
10=125/(x-5)*5/18,
10=125*18/5x-25,
10=2250/5x-25,
10(5x-25)=2250,
50x-250=2250,
50x=2500,
x=50km/hr.
TIME=DISTANCE/RELATIVE SPEED.
Therefore we know that- to convert km/hr to m/s we have to use,
(x-5) * 5/18)m/sec.
TIME=DISTANCE/RELATIVE SPEED
10=125/(x-5)*5/18.
10=TIME,125=DISTANCE,(x-5)*5/18=RELATIVE SPEED
CALCULATION-
10=125/(x-5)*5/18,
10=125*18/5x-25,
10=2250/5x-25,
10(5x-25)=2250,
50x-250=2250,
50x=2500,
x=50km/hr.
Ananya said:
8 years ago
How can the answer be 50 that's the point x-5 would be 40 kmph?
Then how can b be the answer?
Then how can b be the answer?
Gaurav said:
8 years ago
Hey someone tell me, please. Why are you using 18/5 then 5/18?
Because the unit is m/s = 5/18 and you are using 18/5 in this problem.
Because the unit is m/s = 5/18 and you are using 18/5 in this problem.
Saikat Dey said:
8 years ago
Thanks to all for such nice explanations.
Vishu said:
8 years ago
Hey guys for the same question. How to find the time taken by the train to overtake the man. Instead of finding the speed?
Amit thakur said:
8 years ago
Thanks for these explanations.
Paras said:
8 years ago
Hers, x is supposed as speed of train. 5 is substracted because it is relative. Both are going in same direction. If the direction was supposed to be opposite then 5 should have been added.
Dinesh said:
8 years ago
Can you explain relative speed (x-5)?
Akshit mahajan said:
8 years ago
Could anyone tell. Why we had done x-5?
Arbaz said:
8 years ago
Well said @Rahul.
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