Speed
The speed of a moving body is the distance traveled by it in unit time.
Speed =
 Distance travelled Time taken

Distance = speed x time
Conversation of kmph to meter per second:
km/hr =
 5 18
m/sec
m/sec =
 18 5
km/hr
Relative speed:
If two bodies move in the same direction, the relative speed of one with respect to the other is the difference of their speeds.
If two bodies move in opposite direction, relative speed of one with respect to the other body is the sum of their speeds.
Important formulae:
1. If the ratio of the speeds of A and B is a : b, then the ratio of the

the times taken by them to cover the same distance is
 1 a
:
 1 b
or b : a
2. 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.
Stoppage time per hour for a train:
For the same distance of travel, if a train runs at an average speed V1km/hr without stopping and
an average speed of V2km/hr with stoppage then stoppage time per hour =
 V1 - V2 V1
hour
=
 Difference in speed Faster speed
(hour)
Time and distance between two moving bodies:
Let there be two persons A and B
Speed of A = V1km/hr
Speed of B = V2km/hr
If they walk in the same direction, A and B will be (V1 – V2) km apart in 1 hour
Similarly, if they walk in opposite direction, A and B will be (V1 + V2) km apart in 1 hour