Problems on Trains Questions

FACTS  AND  FORMULAE  FOR  PROBLEMS  ON  TRAINS

 

 

1. a km/hr = [a x (5/18)] m/s.

 

2. a m/s = [a x (18/5)] km/hr.

 

3. Time taken by a train of length l metres to pass a pole or a standing man or a signal post is equal to the time taken by the train to cover l metres.

 

4. Time taken by a train of length 1 metres to pass a stationary object of length b metres is the time taken by the train to cover (1 + b) metres.

 

5. Suppose two trains or two bodies are moving in the same direction at u m/s and v m/s, where u > v, then their relatives speed = (u - v) m/s.

 

6. Suppose two trains or two bodies are moving in opposite directions at u m/s and v m/s, then their relative speed = (u + v) m/s.

 

7. If two trains of length a metres and b metres are moving in opposite directions at u m/s and v m/s, then time taken by the trains to cross each other = (a+b)(u+v)sec.

 

8. If two trains of length a metres and b metres are moving in the same direction at u m/s and v m/s, then the time taken by the faster train to cross the slower train = a+bu-vsec.

 

9. 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

Q:

A train sets off at 3 p.m. at the speed of 70 kmph. Another train starts at 4:30 p.m. in the same direction at the rate of 85 kmph. At what time the trains will meet ?

A) 10:10 pm B) 9:50 pm
C) 11:30 pm D) 10:30 pm
 
Answer & Explanation Answer: C) 11:30 pm

Explanation:

Distance = 70 x 1 ½ = 105 km

Relative Speed = 85 – 70 = 15

Time = 105/15 = 7 hrs

4:30 + 7 hrs = 11.30 p.m.

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Q:

Two trains namely X & Y leave station 'A' at 6.30am and 7.40am and travel at 30km/hr and 40 km/hr respectively. How many kms from 'A' will the trains meet ?

A) 140 kms B) 120 kms
C) 96 kms D) 142 kms
 
Answer & Explanation Answer: A) 140 kms

Explanation:

It is given train X leave station A at 6:30 am, here it is asked to calculate the distance from A when the trains meet, the
Distance traveled by train left at 6:30 am upto 7:40 am i.e. in 1 hr. 10 min. or 7/6 hours = 30 x 7/6 = 35 km
So train leaving at 7:40 am will meet first train after covering a distance of 35 km. with relative speed of 40-30=10 km/hr.
Hence time taken = 35/10 = 3.5 hours or 3 hours 30 minutes
So distance from A = Distance traveled by 2nd train in 3 hr. 30 min
= 40 x 3.5 = 140 km.

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Q:

A jogger running at 9 km/hr along side a railway track is 260 m ahead of the engine of a 140 m long train running at 45 km/hr in the same direction. In how much time will the train pass the jogger ?

A) 25 sec B) 40 sec
C) 38 sec D) 32 sec
 
Answer & Explanation Answer: B) 40 sec

Explanation:

Speed of train relative to jogger = 45 - 9 = 36 km/hr.
= 36 x 5/18 = 10 m/sec.

Distance to be covered = 260 + 140 = 400 m.

Time taken = 400/10 = 40 sec.

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Q:

A train moving at 2/3 rd of its normal speed reaches its destination 20 minutes late. Find the normal time taken ?

A) 4/3 hrs B) 2/3 hrs
C) 3/2 hrs D) 1/4 hrs
 
Answer & Explanation Answer: B) 2/3 hrs

Explanation:

Let the original speed and time is S and T
then distance = S x T
Now the speed changes to 2/3S and T is T+20
As the distance is same
S x T = 2/3Sx(T+20)
solving this we get t = 40 minutes
=40/60 = 2/3 hour

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Q:

Find the length of a train if it takes 10 seconds to cross a pole and double of this time to cross a platform of length 200 mts ?

A) 180 mts B) 190 mts
C) 200 mts D) 210 mts
 
Answer & Explanation Answer: C) 200 mts

Explanation:

Let the length of the train be 'L' mts

let the speed of the train be 'S' m/s

Given it crosses a pole in 10 sec=> L/S = 10 ......(1)
Given it takes 20 sec (double of pole) to cross a platform of length 200 mts

=> (L + 200)/S = 20

=> L/S + 200/S = 20

But from (1) L/S = 10

=> 200/S = 20 - 10

=> S = 20 m/s

Then, from (1)

=> L = 10 x 20 = 200 mts.

Hence, the length of the train = 200 mts.

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Q:

Two trains are running at 40 km/hr and 20 km/hr respectively in the same direction. Fast train completely passes a man sitting in the slower train in 5 seconds. What is the length of the fast train?

A) 27 7/9 mts B) 25 8/7 mts
C) 21 1/4 mts D) 22 mts
 
Answer & Explanation Answer: A) 27 7/9 mts

Explanation:
Relative speed = (40 - 20) km/hr = ( 20 x 5 ( m/sec = ( 50 ( m/sec.
18 9
Therefore Length of faster train = ( 50 x 5 ( m = 250 m = 27 7 m.
9 9 9
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Q:

The length of a brigade which a train 130 m long and traveling at 45kmph can cross in 30 seconds, is 

A) 196 mts B) 220 mts
C) 230 mts D) 245 mts
 
Answer & Explanation Answer: D) 245 mts

Explanation:

Let the length of the brigade is x mts
Then Distance = 130 + x mts
given speed = 45 kmph = 45 x5/18 m/s
Time = 30 sec
T = D/S
=> 30 = 130+x/(45x5/18)
=> x = 245 mts.

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Q:

A train 900 m long is running at a speed of 78 km/hr. If it crosses a tunnel in 1 min, then the length of the tunnel is ?

A) 400 m B) 300 m
C) 500 m D) 600 m
 
Answer & Explanation Answer: A) 400 m

Explanation:

Speed = 78 x 5/18 = 65/3 m/sec.
Time = 1 min = 60 sec.
Let the length of the train be x meters.
Then, (900 + x)/60 = 65/3
x = 400 m.

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