Important notes and formula
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.
Distance = Speed x Time
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)
We know 1 km = 1000 m and 1 hour = 3600 seconds.
We know 1000 m = 1 km and 3600 seconds = 1 hour.
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
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
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