14
Q:

Two trains of equal length , running in opposite directions , pass a pole in 18 and 12 seconds. The trains will cross each other in 

A) 14.4 sec B) 15.5 sec
C) 18.8 sec D) 20.2 sec

Answer:   A) 14.4 sec



Explanation:

Let the length of the train be L metres

Speed of first train = \inline \frac{3600}{18}\times L m/hour

Speed of secxond train = \inline \frac{3600}{12}\times L m/hour

When running in opposite directions, relative speed = 200 L + 300 L m/hour

Distance to be covered = L + L = 2L metre

Time taken = \inline \frac{2L}{500L}\times 3600 sec

                 =14.4 sec

Q:

A train is moving and crossing a man who is running on a  platform of 100 m at a speed of 8 kmph in the direction of the train, in 9 sec. If the speed of the train is 74 kmph. Find the length of the train ?

A) 202 mts B) 188 mts
C) 165 mts D) 156 mts
 
Answer & Explanation Answer: C) 165 mts

Explanation:

Let the length of the train = L mts

Relative speed of train and man = 74 - 8 = 66 kmph = 66 x 5/18 m/s

=> 66 x 5/18 = L/9

=> L = 165 mts.

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8 121
Q:

A train travelling at 48 kmph crosses another train, having half its length and travelling in opposite direction at 42 kmph, in 12 sec. It also covers a bridge in 45 sec. Find the length of the bridge ?

A) 250 mts B) 400 mts
C) 320 mts D) 390 mts
 
Answer & Explanation Answer: B) 400 mts

Explanation:

Let the length of the 1st train = L mts

Speed of 1st train = 48 kmph

Now the length of the 2nd train = L/2 mts

Speed of 2nd train = 42 kmph

Let the length of the bridge = D mts

Distance = L + L/2 = 3L/2

Relative speed = 48 + 42 = 90 kmph = 90 x 5/18 = 25 m/s(opposite)

Time = 12 sec

=> 3L/2x25 = 12

=> L = 200 mts

Now it covers the bridge in 45 sec

=> distance = D + 200

Time = 45 sec

Speed = 48 x5/18 = 40/3 m/s

=> D + 200/(40/3) = 45

=> D = 600 - 200 = 400 mts

Hence, the length of the bridge = 400 mts.

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5 198
Q:

The difference between the time taken by two trains to travel a distance of 350 km is 2 hours 20 minutes. If the difference between their speeds is 5 km/hr, what is the speed of faster train ?

A) 36 kmph B) 30 kmph
C) 34 kmph D) 40 kmph
 
Answer & Explanation Answer: B) 30 kmph

Explanation:

Let the speed of the faster train be 'S' kmph

Then speed of the slower train will be '(S-5)' kmph

Time taken by faster train = 350/S hrs

Time taken by slower train = 350/(S-5) hrs

=> S = 30 km/hr.

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5 295
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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5 392
Q:

The length of two superfast trains are 140 mts and 160 mts respectively. If they run at the speed of 60 km/hr and 80 km/hr respectively in opposite direction, find the time in which they will cross each other ? 

A) 7.71 sec B) 10.48 sec
C) 9.36 sec D) 8.45 sec
 
Answer & Explanation Answer: A) 7.71 sec

Explanation:

Given L1 = 140 m

L2 = 160 m

S1 = 60 km/hr

S2 = 80 km/hr

From the question we get,

S1 + S2 = (L1 + L2) / T

=> (60 + 80) 5/18 m/s = 140 + 160/T

=> T = 54/7 = 7.71 sec

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