Question

How long does a train 110 meters long running at a speed of 72 km/hr take to cross a bridge 132 meters in length?

Answer 1

Speed = 72km/hr
         
           = 72 * 1000
               60* 60
           = 72 * 5
                    18
           = 20m/s

Total distance = 110 + 132
                      = 242 meters

Time = Distance / speed

Time = 242 / 20

Time = 12.1 seconds.

So the train takes 12.1 seconds to cross the bridge.

Answer 2

Given:

• Length of the train = 110 m
• Length of the bridge = 132 m
• Speed of the train = 72 Km/hr

To Find:

• Total time taken by the train to cross the bridge.

Solution:

The total distance of the train = 132 + 110 = 242 m because the train must cross the length of the bridge with its own length.

Speed = 72 Km/hr

We should convert the SI unit of the speed to m/s as the other values are given in the same SI unit.

⇒ Speed = 72 Km/hr = 72×1000 m/hr = 72,000m/hr { here, 1m = 1000 Km}

⇒ Speed = 72,000/360 m/s = 20 m/s { 1 hr = 360 s}

We know that,

⇒ Speed = distance / time

rearrange the above equation to find the value of time.

⇒ time = distance/speed = 242/20 = 12.1 s

⇒ time = 12.1 s

∴ Total time taken by the train to cross the bridge = 12.1 s