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**Problems on Trains:**

- a km/hr = a*(5/18) m/s
- a m/s = a*(18/5) km/hr
- 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.
- Time taken by a train of length l metres to pass a stationary object of length b metres is the time taken by the train to cover (l + b) metres.
- 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 relative speed = (u – v) m/s.
- Suppose two trains or two bodies are moving in the opposite direction at u m/s and v m/s, then their relative speed is = (u + v) m/s.
- 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.
- If two trains of length a metres and b metres are moving in same directions at u m/s and v m/s, then time taken by the f*er train to cross the slower train = (a+b)/(u-v) sec.
- If two trains 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 )

**Aptitude Questions:**

1. A train moves with a speed of 108 kmph. Its speed in metres per second is:

A) 10.8

B) 18

C) 30

D) 38.8

E) None of these

View Answer

Answer: option C

Explanation:

108 kmph = (108*5/18) m/s = 30 m/sec

2. A train 280 m long, running with a speed of 63 km/hr will pass a tree in:

A) 15 sec

B) 16 sec

C) 18 sec

D) 20 sec

E) None of these

View Answer

Answer: option B

Explanation:

Speed = (63*5/18) m/sec = 35/2 m/sec

Time taken = (280*2/35) sec = 16 sec

3. A train running at the speed of 60 km/hr crosses a pole in 9 seconds. What is the length of the train?

A) 120 metres

B) 180 metres

C) 324 metres

D) 150 metres

E) None of these

View Answer

Answer: option D

Explanation:

Speed = (60*5/18) m/sec = 50/3 m/sec

Length of the train = (speed * time) = (50/3*9) m = 150 m

4. A train covers a distance of 12 km in 10 minutes and if it takes 7 seconds to pass a pole, then the length of the train is:

A) 90 m

B) 100 m

C) 120 m

D) 140 m

E) None of these

View Answer

Answer: option D

Explanation:

Speed = (12/10 * 60) km/hr = (72 * 5/18) m/sec = 20 m/sec

Length of the train = (speed * time) = (20 * 7) m = 140 m

5. The length of the bridge, which a train 140 metres long and travelling at 45 km/hr can cross in 30 seconds, is:

A) 200 m

B) 225 m

C) 235 m

D) 250 m

E) None of these

View Answer

Answer: option C

Explanation:

Speed = (45 * 5/18) m/sec = 25/2 m/sec; Time = 30 sec

Let the length of bridge be x metres.

Then, (140+x) / 30 = 25/2 <=> 2(140 + x) = 750 <=> x = 235 m