Train A takes 10 seconds to cross a pole and 20 seconds to cross a pla

1.	Train A takes 10 seconds to cross a pole and 20 seconds to cross a platform of 100m. Train B which moves in the opposite direction to train A is moving at a speed of 72 kmph. Calculate relative speed1. 136 kmph2. 144 kmph3. 90 kmph4. 108 kmph
Answer» Correct Answer - Option 4 : 108 kmph Given: Crosses pole = 10 seconds and platform = 20 seconds Platform = 100 m Formula used: Speed = Distance / time 1 kmph = 5/18 m/s Calculation: Form two equations by assuming length of train L and speed S ⇒ Pole: 10 = D / S ⇒ 10 S = D …..(1) ⇒ Platform: 20 = (D + 100) / S ⇒ 20S = D + 100 ⇒ 20S = 10S + 100 ….(From (1)) ⇒ 10 S = 100 ⇒ S = 10 m/s Converting m/s to kmph ⇒ 10 m/s = 10 × 18 / 5 ⇒ S = 36 kmph Relative speed = Speed 1 + Speed 2 ⇒ Relative speed = 36 + 72 ⇒ Relative speed = 108 kmph ∴ Relative speed is 108 kmph

Train A takes 10 seconds to cross a pole and 20 seconds to cross a platform of 100m. Train B which moves in the opposite direction to train A is moving at a speed of 72 kmph. Calculate relative speed1. 136 kmph2. 144 kmph3. 90 kmph4. 108 kmph

Answer» Correct Answer - Option 4 : 108 kmph

Given:

Crosses pole = 10 seconds and platform = 20 seconds

Platform = 100 m

Formula used:

Speed = Distance / time

1 kmph = 5/18 m/s

Calculation:

Form two equations by assuming length of train L and speed S

⇒ Pole: 10 = D / S

⇒ 10 S = D …..(1)

⇒ Platform: 20 = (D + 100) / S

⇒ 20S = D + 100

⇒ 20S = 10S + 100 ….(From (1))

⇒ 10 S = 100

⇒ S = 10 m/s

Converting m/s to kmph

⇒ 10 m/s = 10 × 18 / 5

⇒ S = 36 kmph

Relative speed = Speed 1 + Speed 2

⇒ Relative speed = 36 + 72

⇒ Relative speed = 108 kmph

∴ Relative speed is 108 kmph

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