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.

## Finding Distance and Time

Distance = Speed x Time

## 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,

## Convert m/s to km/hr

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

Therefore,

## 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