Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 28)
28.
A train overtakes two persons walking along a railway track. The first one walks at 4.5 km/hr. The other one walks at 5.4 km/hr. The train needs 8.4 and 8.5 seconds respectively to overtake them. What is the speed of the train if both the persons are walking in the same direction as the train?
Answer: Option
Explanation:
| 4.5 km/hr = |  |
4.5 x | 5 |  |
m/sec = | 5 | m/sec = 1.25 m/sec, and |
| 18 | 4 |
| 5.4 km/hr = | |
5.4 x | 5 | |
m/sec = | 3 | m/sec = 1.5 m/sec. |
| 18 | 2 |
Let the speed of the train be x m/sec.
Then, (x - 1.25) x 8.4 = (x - 1.5) x 8.5
8.4x - 10.5 = 8.5x - 12.75
0.1x = 2.25
x = 22.5
 Speed of the train = |
|
22.5 x | 18 | |
km/hr = 81 km/hr. |
| 5 |
Discussion:
54 comments Page 2 of 6.
Gowthami said:
1 decade ago
@Gowthami
4.5km/hr=4.5x5m/sec =5m/sec=1.25m/sec
5.4km/hr=5.4x5m/sec=3m/sec=1.5m/sec
then speed of the train=x
distance=speed*time
so distance=(x-1.25)*8.4-------------1
distance=(x-1.5)*8.5----------------2
(1)=(2)
(x - 1.25) x 8.4 = (x - 1.5) x 8.5
4.5km/hr=4.5x5m/sec =5m/sec=1.25m/sec
5.4km/hr=5.4x5m/sec=3m/sec=1.5m/sec
then speed of the train=x
distance=speed*time
so distance=(x-1.25)*8.4-------------1
distance=(x-1.5)*8.5----------------2
(1)=(2)
(x - 1.25) x 8.4 = (x - 1.5) x 8.5
John said:
9 years ago
@Saurav 5/18 is the common unit to convert speed by km/hr to m/s. But the question is distance calculated can't be equal because both the persons having different speed and most probably they can't be at the equal level or abreast.
Yaswanth said:
1 decade ago
Hi Vinay, the distance here is the length of train.... Consider the human as a point. Then length of train from case 1 is 8.4(x-1.25) and from case 2 is 8.5(x-1.5)...
Since the length of train is constant...
We can equate both.
Since the length of train is constant...
We can equate both.
Nitesh Nandwana said:
1 decade ago
Hi Chanda,
If two trains (or bodies) start at the same time from points A and B towards each other and after crossing they take a and b sec in reaching B and A respectively, then:
(A's speed) : (B's speed) = (b : a)
If two trains (or bodies) start at the same time from points A and B towards each other and after crossing they take a and b sec in reaching B and A respectively, then:
(A's speed) : (B's speed) = (b : a)
Harshad said:
1 decade ago
@Siva.
The length of the train is the distance.
In our case its (x - 1.25) x 8.4 OR (x - 1.5) x 8.5.
When we equate we got x = 22.5.
So substitute in any equation.
And we get length as 178.5 m.
The length of the train is the distance.
In our case its (x - 1.25) x 8.4 OR (x - 1.5) x 8.5.
When we equate we got x = 22.5.
So substitute in any equation.
And we get length as 178.5 m.
Nitishkumar said:
1 decade ago
The two train and man are moving in same direction.
So the relative speed = x-5.4 & another we write that other man, x-4.5 train length is constant that's by distance will be equal.
So the relative speed = x-5.4 & another we write that other man, x-4.5 train length is constant that's by distance will be equal.
Gururaj said:
1 decade ago
But the two man is also moving then there is change in distance, so how then (x-1.25)x8.4=(x-1.5)x8.5 both are moving so both the distance are varying.
Can some one please explain this?
Can some one please explain this?
Gowthami said:
1 decade ago
Hi Deepika
The last step is converting m/sec to km/hr.
But i am not understanding how can the dist be equated?
(x - 1.25) x 8.4 = (x - 1.5) x 8.5
can any one explain it plz.
The last step is converting m/sec to km/hr.
But i am not understanding how can the dist be equated?
(x - 1.25) x 8.4 = (x - 1.5) x 8.5
can any one explain it plz.
Suan said:
1 decade ago
We don't necessarily have to use the conversion of kmph to m/s here since the unnecessary units (sec) eventually cancel out each other on the subsequent steps of solution.
Haphyz said:
1 decade ago
Since we are calculating relative speeds, the value of the distance can only imply the length of the train which is constant. Hence the need to equate both distances.
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers