Two trains 140 m and 160 m long run at the speed of 60 km/hr and 40 km/hr respectively in opposite directions on parallel tracks. The time (in seconds) which they take to cross each other, is:

Correct Answer: 36 kmph

Explanation:

Given speed of the first train = 60 km/hr = 60 x 5/18 = 50/3 m/s

Let the speed of the second train = x m/s

Then, the difference in the speed is given by

50 3 - x = 120 18

=> x = 10 m/s

=> 10 x 18/5 = 36 km/hr

Correct Answer: 50 kms

Explanation:

Let the distance be 'd' kms.

According to the given data,

$$\begin{gathered} d 30 - d 50 = 40 60 hrs \\ = > 6 d = 300 \\ = > d = 50 kms . \\ \end{gathered}$$

Correct Answer: 230 m

Explanation:

Relative speed = (120 + 80) km/hr

=(200*5/18)m/s = (500/9)m/s

 

Let the length of the other train be x metres.

 

Then, x+270/9 = 500/9 

 

=>  x + 270 = 500

 

=>  x = 230.

Correct Answer: 12

Explanation:

Speed of train 1 =  120 10 m / s e c = 12 m/sec 

Speed of train 2 = 120 15 m / s e c  = 8 m/sec 

if they travel in opposite direction, relative speed = 12 + 8 = 20 m/sec

distance covered = 120 + 120 = 240 m

time = distance/speed = 240/20 = 12 sec

Correct Answer: 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.

Correct Answer: 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.

Correct Answer: 60 kms

Explanation:

Let 'd' be the distance and 's' be the speed and 't' be the time
d=sxt
45 mins = 3/4 hr and 48 mins = 4/5 hr
As distance is same in both cases;
s(3/4) = (s-5)(4/5)
3s/4 = (4s-20)/5
15s = 16s-80
s = 80 km.
=> d = 80 x 3/4 = 60 kms.

Correct Answer: 270 m

Explanation:

Speed =[ 72 x (5/18) ]m/sec= 20 m/sec.

Time = 26 sec.

Let the length of the train be x metres.

Then,[ (x+250)/26 ]= 20

=> x + 250 = 520

=> x = 270.

Correct Answer: 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

  350 s - 5 - 350 s = 2 h r s 20 m i n = 2 1 3 = 7 3

 

=> S = 30 km/hr.

Correct Answer: 500