Speed Distance and Time

Aptitude

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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

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