Speed, Time and Distance
 How much time does a train, 50 m long, moving at 68 km/ hour take to pass another train, 75 m long, moving at 50 km/hour in the same direction ?

 5 seconds
 10 seconds
 20 seconds
 25 seconds

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Both trains are moving in the same direction.
∴ Their relative speed
= (68 – 50) kmph = 18 kmph= 18 × 5 = 5 m/sec 8
Total length = 50 + 75 = 125 m∴ Required time = Total length Relative speed = 125 = 25 seconds. 5 Correct Option: D
Both trains are moving in the same direction.
∴ Their relative speed
= (68 – 50) kmph = 18 kmph= 18 × 5 = 5 m/sec 8
Total length = 50 + 75 = 125 m∴ Required time = Total length Relative speed = 125 = 25 seconds. 5
 A constable is 114 metres behind a thief. The constable runs 21 metres and the thief runs 15
metres in a minute. In what time will the constable catch the thief ?

 19 minutes
 18 minutes
 17 minutes
 16 minutes

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The gap of 114 metre will be filled at relative speed.
Required time = 114 minutes 21 − 15 = 114 = 19 minutes 6 Correct Option: A
The gap of 114 metre will be filled at relative speed.
Required time = 114 minutes 21 − 15 = 114 = 19 minutes 6
 A moving train, 66 metres long, overtakes another train of 88 metres long, moving in the same direction in 0.168 minutes. If the second train is moving at 30 km/hr, at what speed is the first train moving ?

 85 km/hr.
 50 km/hr.
 55 km/hr.
 25 km/hr.

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Suppose the speed of first train be x kmph
Speed of second train = 30 kmph= 3 × 1000 = 500 m per min. 60
∴ According to questionTotal Distance Relative speed = (66 + 88) = 0.168 x − 500 ⇒ 154 = 0.168 x − 500
⇒ 0.168x – 84 = 154
⇒ 0.168x = 238⇒ x = 238 0.168 = 238 × 1000 m per minute 168 = 238 × 1000 × 3 kmph 168 50
= 85 kmphCorrect Option: A
Suppose the speed of first train be x kmph
Speed of second train = 30 kmph= 3 × 1000 = 500 m per min. 60
∴ According to questionTotal Distance Relative speed = (66 + 88) = 0.168 x − 500 ⇒ 154 = 0.168 x − 500
⇒ 0.168x – 84 = 154
⇒ 0.168x = 238⇒ x = 238 0.168 = 238 × 1000 m per minute 168 = 238 × 1000 × 3 kmph 168 50
= 85 kmph
 A thief is noticed by a policeman from a distance of 200m. The thief starts running and the policeman chases him. The thief and the policeman run at the rate of 10 km./hr and 11 km./hr respectively. What is the distance between them after 6 minutes ?

 100 m
 190 m
 200 m
 150 m

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Relative speed of police
= 11 – 10 = 1 kmph= 5 m/sec 18 ∴ Distance decreased in 6 minutes = 5 × 6 × 60 18
= 100 m
∴ Distance remained between them = 200–100 = 100 mCorrect Option: A
Relative speed of police
= 11 – 10 = 1 kmph= 5 m/sec 18 ∴ Distance decreased in 6 minutes = 5 × 6 × 60 18
= 100 m
∴ Distance remained between them = 200–100 = 100 m
 The speeds of three cars are in the ratio of 1 : 3 : 5. The ratio among the time taken by these cars to travel the same distance is

 3 : 5 : 15
 15 : 3 : 5
 15 : 5 : 3
 5 : 3 : 1

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Speed ∝ 1 Time ∴ Required ratio of time = 1 : 1 : 1 3 5 = 15 : 1 × 15 : 1 × 15 3 5
= 15 : 5 : 3Correct Option: C
Speed ∝ 1 Time ∴ Required ratio of time = 1 : 1 : 1 3 5 = 15 : 1 × 15 : 1 × 15 3 5
= 15 : 5 : 3