A train, travelling at `20 km//hr` is approaching a platform. A bird is sitting on a pole on the platform. When the train is at a distance of 2 km from pole, breakes are applied which produce auniform deceleration in it. At that instant the bird flies towards the train at `60 km//hr` and after touching the nearest point on the train flies back to the pole and then flies towards the train and continues repeating itself. Calculate how much distance will the bird have flown before the train stops?

Explanation

For retardation of train `v^(2)=u^(2)+2as`
`rArr 0=(20)^(2)+2(a)(2)rArr a=-100 kmh^(-2)`
Time required to stop the train
`v=u+at rArr 0=20-100t rArr t=(1)/(5)h`
For bird, speed `=("Distance")/("Time")rArr s_(B)=v_(B)xxT=60xx(1)/(5)=12 km`