RRB NTPC - Problems on Trains

6.

Two trains are running in opposite directions with the same speed. If the length of each train is 120 metres and they cross each other in 12 seconds, then the speed of each train (in km/hr) is:  

   A.) 10
   B.) 18
   C.) 72
   D.) 36

Answer: Option 'D'

Given, Length of each train = 120 metres.
Let the speed of each train be x m/sec.
Then, relative speed of the two trains = x + x = 2x m/sec.
So, Speed = Distance / Time
=> Relative Speed of two trains = (Sum of length of two trains) / Time taken to cross each other.
=> 2x = (120 + 120 ) / 12
=> 2x = 20
=> x = 10.
Therefore,Speed of each train = 10 m/sec = ( 10 x 18/5 ) km/hr = 36 km/hr.

7.

A train is running at 108 Kmph. It was crossed an electronic pole in 28sec. find the length of the train? 

   A.) 480m
   B.) 840m
   C.) 640m
   D.) 740m

Answer: Option 'B'

L = S × T 
L = 108 Kmph × 28Sec 
L =108 × 5/18 × 28 
L= 840m

8.

A train 360 m long is running at a speed of 45 km/hr. In what time will it pass a bridge 140 m long?

   A.) 48 seconds
   B.) 42 seconds
   C.) 40 seconds
   D.) 45 seconds

Answer: Option 'C'

Given, Length of train =360 m
Length of bridge =140 m
Speed of train = 45 km/hr ---> Converting into meter/ second
= 45 × (5/18) m / sec
= 12.5 m/sec
=>Speed of train =12.5 m/sec
Required Time =(Length of train + Length of bridge) /Speed of train
= (360 + 140) / 12.5
= 500 / 12.5
= 40 sec
=>Required Time =40 sec

9.

A train passes a station platform in 36 seconds and a man standing on the platform in 20 seconds. If the speed of the train is 54 km/hr, what is the length of the platform?

   A.) 120 m
   B.) 240 m
   C.) 300 m
   D.) 250 m

Answer: Option 'B'

Given,speed of the train = 54 km/hr
---> converting this speed into meter/ sec
=> Speed of the train = (54 x 5 / 18 ) m/sec = 15 m/sec
Given that, thetrain passesa man in 20 seconds.
=> Length of the train = speed of the train *Time to pass theman 
= 15 × 20
300 meter
Given that, thetrain passesa platform in 36 seconds.
=> Length of the train + Length of the platform = speed of the train × Time to pass the platform
=> 300 + Length of the platform = 15 × 36
=>Length of the platform = 540 - 300
=>Length of the platform = 240 meter.

10.

A train 240 m long passes a pole in 24 seconds. How long will it take to pass a platform 650 m long? 

   A.) 65 sec
   B.) 89 sec
   C.) 100 sec
   D.) 150 sec

Answer: Option 'B'

Given, length of the train = 240 m
Time taken by the train to pass the pole = 24 sec
Length of the Platform = 650 m
To find theTime taken by the train to pass the platform:-
Speed of the train = length of the train /Time taken by the train to pass the pole
= (240/ 24 )
= 10 m/sec.
Therefore, Time taken by the train to pass the platform = (length of the train + Length of the Platform) / Speed of the train
= [(240 + 650) / 10] sec
89 sec

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