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If a train crosses a platform of 110 m long in 13.5 sec and also crosses another platform of 205 m long in 18.25 sec, what will be the speed of the train in km/hour?
- A60 km/h
- B72 km/h
- C65.5 km/h
- D75 km/h
Answer not set
Discussion 1
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Let the length of the train is 'x' meters and the speed of the train is 's' m/s.
When it crosses the first platform,
(x + 110)/s = 13.5
⇒ x + 110 = 13.5s
⇒ x = 13.5s – 110 ----(1)
And when it crosses the second platform,
(x + 205)/s = 18.25
⇒ x + 205 = 18.25s
From equation (1), we get
13.5s – 110 + 205 = 18.25s
⇒ 4.75s = 95
⇒ s = 95/4.75
⇒ s = 20 m/s = 20 × 18/5 km/h = 72 km/h
∴ Speed of the train is 72 km/h.
When it crosses the first platform,
(x + 110)/s = 13.5
⇒ x + 110 = 13.5s
⇒ x = 13.5s – 110 ----(1)
And when it crosses the second platform,
(x + 205)/s = 18.25
⇒ x + 205 = 18.25s
From equation (1), we get
13.5s – 110 + 205 = 18.25s
⇒ 4.75s = 95
⇒ s = 95/4.75
⇒ s = 20 m/s = 20 × 18/5 km/h = 72 km/h
∴ Speed of the train is 72 km/h.