problem for train and stream

PROBLEMS ON TRAIN AND BOAT 4 PSC

Problems on Trains

Time taken by train of lenght L to pass a point is same as time taken by train to travel a distance L

Time taken by train of length L to pass an object of lenght  B is same as time taken by train to travel a distance L+B

Suppose  two train or bodies are trsvelling in opposite direction with speeds  u and v_, then their relative speeds os (u+v).

Suppose two trains or bodes are travelling in the same direction with speeds u and v (u> v), then their relative speed is (u-v)

Suppose two trains or bodies of lenght a and b metres are travelling in opposite direction with speeds u m/sand V m/s , then  time taken by trains to cross each other =   (a+b)

                                                                                                                             u+v

Suppose two trains or bodies of lenght a and b metres are travelling in the same direction with speeds  u m/s and v m/s, then time taken by the faster train to cross the slower train =(a+b)

                                                                                                                                                u-v

If  two trains or bodies start at point A and B to wards each other and after crossing they take a and b sec in reaching B and A repectively, then (A’s speed): (B’s speed)=  :  ,

Boats and Streams

If speed of a boat in still water is u km/hr and the speed of the stream is v km/hr,then the speed of the boat upstream is (u-v) km/hr and the speed of boat downstream is (u+v) km/hr.

If the speed of the boat downstream is km/hr and upstream is b km/hr; then the speed of the boat in still water is   (a+b) and the speed of the stream is   1/2 (a-b)