Speed Distance and Time

Important notes and formula

Relation between speed, distance and time

If a car travels D distance in time T then we say the speed of the car is S and we express the speed in terms of distance and time as follows.

Speed =	Distance
	Time

Finding Distance and Time

Distance = Speed x Time

Time =	Distance
	Speed

Unit of speed

Speed is expressed as distance per unit time. Most commonly used unit for speed are
meter per second (m/s)
kilometer per hour (km/hr)

Convert km/hr to m/s

We know 1 km = 1000 m and 1 hour = 3600 seconds.
Therefore,

1 km/hr =	1000	m/s
	3600

1 km/hr =	5	m/s
	18

Convert m/s to km/hr

We know 1000 m = 1 km and 3600 seconds = 1 hour.
Therefore,

1 m/s =	18	km/hr
	5

Speed Ratio

If the speed of two trains are in the ratio X:Y then time taken by them to cover the same distance is Y:X

Travelling same distance but at a different speed

If a car covers a certain distance at a speed X km/hr and then covers an equal distance at Y km/hr then the average speed of the car for the complete journey is

Avg. Speed =	2XY
	X+Y