Two trains are moving in the opposite direction on parallel tracks at

Question

Two trains are moving in the opposite direction on parallel tracks at the speeds of 60 km/hr and 90 km/hr respectively. The first train passes a telegraph post in 5 seconds whereas the second train passes the post in 6 seconds. What is the time taken (in seconds) by the trains to cross each other completely?

A. 5
B. 5.2
C. 5.4
D. 5.6
E. 5.8

A. 5
B. 5.2
C. 5.4
D. 5.6
E. 5.8

Mohammadmo · Answer

At the first we've got to find the length of each train: 
T1: (60/3600)×5= 5/60km
T2: (90/3600)×6= 6/40km
Because it's train is moving towards each other, so , we must calculate the total of speed.
V1: 1/60kms
V2: 1/40kms
(1/60 + 1/40)×t=(5/60 + 6/40)
==» t= (28/120) ÷(5/120)
t= 28/5= 5.6s
Option D

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mukherjeeabhish · Answer

Length of the train / Time = Speed

For Train 1 - Length = 5 * 60 * 5 /18 = 250/3

For Train 2 - Length = 6 *90*5/18 = 150

To cross each other total distance covered = Length of both the trains

So time = (250/3 + 150 ) / (60+90) * 5/18 = 28 /5 = 5.6

Ans- D

rgreenhill · Answer

S = D/T

I simplify the train speeds using rations because it simplifies the calculations.
Train 1 = 2
Train 2 = 3

Calculate train lengths using S*T = D:
Train 1: 
2*5 = 10

Train 2:
3*6 = 18

Total length = 10+18 = 28
Total speed = 3+2 = 5

Total time using T = D/S: 28/5 =5.6

D

DivyanshSinghBais · Answer

Given Data:
**Speed of Train 1 & 2 in kmph: 
S1 = 60kmph ; S2 = 90Kmph; 
or 
S1 = 50/3 m/s ; S2 = 25 m/s;

**Time of Train 1 & 2 to cross a (Telegraph/Pole/standing man) is 5secs & 6 secs
**Find L1 & L2:
5 = L1 / (50/3) >> L1 = 250/3 mtrs;
6 = L2 / (25) >> L2 = 150 mtrs;
 
Time for trains to cross each other in opposite direction 
=> (L1 + L2) / (S1 + S2) 
=> (250/3 + 150) / (50/3 + 25)
=> 28/5 => 5.6
 
Hence, Ans is D

Scuven · Answer

I resolved the problem in this way:

1) Since the train which travels at 60 km/h and the time to pass a telegraph is 5 seconds the estimate coefficient is 60/5 (s=v/t) = 12 (i did not convert the speed in km/s since i will reason with relative values and the number level in my opinion is not relevant)

2) Since the train which travels at 90 km/h and the time to pass a telegraph is 6 seconds the estimate coefficient is 90/6 (s=v/t) = 15

3) Then we reason as a weighted average time with weights on space travelled (12/(12+15))*5 + (15/(12+15))*6 = which is approximately 5.6 -> D

Is this reasoning correct? I'm not so sure even though I reach the result

ScottTargetTestPrep · Answer

Solution:

First, we need to determine the lengths of each train. Since the first train is traveling at the speed of 60 km/hr and passes a telegraph post in 5 seconds or 5/3600 = 1/720 hour, the length of the first train is 60 x 1/720 = 1/12 km. Similarly, since the second train is traveling at the speed of 90 km/hr and passes a telegraph post in 6 seconds or 6/3600 = 1/600 hour, the length of the second train is 90 x 1/600 = 3/20 km. Now, we can create the equation where t is the time (in hours) needed for the trains to cross each other completely.

60t + 90t = 3/20 + 1/12

150t = 9/60 + 5/60

150t = 14/60

t = (7/30)/150 = 7/4500

We see that it takes the trains 7/4500 hour, or 7/4500 x 3600 = 5.6 seconds, to cross each other completely.

Answer: D

Kinshook · Answer

Given: Two trains are moving in the opposite direction on parallel tracks at the speeds of 60 km/hr and 90 km/hr respectively. The first train passes a telegraph post in 5 seconds whereas the second train passes the post in 6 seconds. 
Asked: What is the time taken (in seconds) by the trains to cross each other completely?

Length of the first train = 60*(5/18)*5 = 250/3 m
Length of the second train = 90*(5/18)*6 = 150 = 450/3 m
Total length of the trains = 700/3 m
Relative speed of the trains running in opposite direction = 60 + 90 = 150 kmh = 150*(5/18) = 125/3
Time taken to cross each other completely = (700/3)/(125/3) = 5.6 s

IMO D

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