Question

A 100 m long train is going at a speed of 60 km/hr It will cross a 140 m long railway bridge in
1) 3.6 sec
2) 7.2 sec
3) 14.4 sec
4) 21.6 sec​

Answer 1

3) 14.4 seconds

Explanation:

The length of the train is 100 m.

The length of the bridge is 140 m.

To cross the bridge the train have to totally cover a distance of = (100+140)m

                                                                                                        = 240 m.

Hence, total distance = 240 m.

The speed of the train is 60 km/hr.

∴ The speed of the train in m/s = (60×5/18)

                                                    =(10×5/3)

                                                    =(50/3) m/s

(50/3) m is covered by the train in 1 second.

∴ 1 m is covered by the train in (3/50) second.

∴ 240 m is covered by the train in (240×3/50) second

                                                        =(24×3/5) seconds

                                                         = (72/5) seconds

                                                        = 14.4 seconds.

∴ The train will take 14.4 seconds to cross the bridge.