EXAMSPIRE: Distance Time and Speed

Relation between time distance and speed

Relation between time distance and speed is given by the equationsSpeed=Distance/Time
or
Distance=Speed*Time
or
Time=Distance/Speed

Unit of speed is km/hr or m/s

If speed is given in km/hr,then inorder to convert it in to m/s multiply by 5/18

1km/hr=5/18m/s

If speed is given in m/s,then inorder to convert it in to km/hr multiply by 18/5

If ratio of speed of two moving object is a:b, then ratio between times taken for covering same distance is b:a.
If two objects A and B moving in opposite direction from two different places reach at common point in t1 and t2 hrs respectively ,Then Speed of A:Speed of B=sqrt(t2/t1)

average speed=total distance/total time taken.
If a moving object covers a certain distance with a speed of x km/hr and again covers same distance with a speed of ykm/hr, then average speed is 2xy/(x+y).
If a moving object covers a certain distance with a speed of x km/hr and again covers same distance with a speed of ykm/hr and again with zkm/hr,then average speed is=3xyz/(xy+yz+xz)

If two trains are travelling in same direction ,then their relative speed is equal to difference of their speeds.Then Time taken by the fast train to cross the slower train is =Sum of lengths of both trains/difference of their speed
If two trains are travelling in opposite direction ,then their relative speed is equal to sum of their speeds.Then time taken to pass one another is =Sum of lengths of both trains/sum of their speed.
when a train is clearing a pole or a point, then distance covered by train is equal to its length
When a train is covering a platform or bridge or tunnel ,then distance covered by train is equal to sum of the length of train and the length of platform/tunnel/bridge.
When a moving train crosses another train, then distance covered is equal to sum of lengths of both trains.

If speed of stream=xkm/hr and speed of boat in still water is ykm/hrthen speed of boat in downstream=x+y km/hr ,speed of boat in upstream=y-x km/hr
If speed of boat in upstream and speed of boat in down stream is given then, speed of boat in still water=1/2(speed in upstream+speed in downstream) , speed of stream=1/2(Speed in downstream - speed in upstream)