The distance covered in a unit time interval is known as speed. It is obtained by dividing the distance covered by an object by the time it takes to cover that distance.

Speed= (Distance/Time)

Time

Time= (Distance/Speed)

Distance

Distance= (Speed*Time)

km/hr to m/sec conversion:

x km/hr = ( x* 5/18 )m/sec.

m/sec to km/hr conversion:

x m/sec= ( x* 18/5 )km/hr.

If the ratio of the speeds of A and B is a:b, then the ratio of the
times taken by then to cover the same distance is 1/a:1/b or b:a.
Suppose a man covers a certain distance at x km/hr and an equal distance at y km/hr. Then, the average speed during the whole journey is (2xy/x+y) km/hr.

RELATIVE SPEED

Case 1: Two bodies are moving in opposite directions at speed V1 & V2 respectively. The relative speed is defined as Vr = VI + V2.

Case 2: Two bodies are moving in same directions at speed VI. & V2 respectively,The relative speed is defined as Vr = |VI -V2|.

Circular Motion

The relative velocity of 2 bodies moving around a circle in the same direction is taken as (V1- V2) and while moving in opposite direction is taken as (V1+V2).

First Meeting Three or more bodies start moving simultaneously from the same point on the circumference of the circle . They will 1st meet again in the Lai of the times that the fastest runner will takes in totally overlapping each of the slower runners .

First meeting time = Circumference / Relative velocity

First Meeting at starting point The first meeting at the starting point will occur after a time that is obtained by the LCM of the times that each of the bodies takes the complete one full round.