Question

Annabelle is taking the train to see her boyfriend on valentine's day! The train is 100 metres long and it takes 30 sec to cross a 400 m bridge.what speed is the train going at?

Answer 1

The length of train is added in distance because time is measured from 'when the train gets on the bridge' to 'when the train leaves the bridge'

Finding speed in metre/s

Distance = 400m + 100m (Length of train)
               = 500m

Time       = 30 seconds
Speed = Distance / Time
            = 500 /30
            = 16.6667 metre/s

Finding speed in km/hr

Distance= 400 metre + 100 metre (Length of train)
              = 500 metre
              = 500/1000 km
              = 0.5 km

Time = 30 seconds
         = 30/(60*60)
         = 30/3600
         = 0.008333...

Speed = D/T
           = 0.5/0.008333
           =  60.0024 Km/hr