# Speed, Distance and Time

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Distance covered in unit time is known as speed.

Speed = Distance/Time

Some units of speed are km/hr, m/min, m/sec and cm/sec.

If the distance covered is constant, then the speed is inversely proportional to the time taken.

If the speed is constant, then the time taken is proportional to the distance.

If time taken is constant, then the speed is proportional to the distance covered.

If an object covers equal distance in equal intervals of time, then it is said to travel with a uniform speed.

If an object covers different distances in equal intervals of time, then it is said to travel with a variable speed.

Average speed of any object is equal to the total distance travelled upon total time taken.

Speed of one object with respect to another is called the relative speed.

If two objects move in the same direction, then their relative speed is equal to the difference of their speeds.

If two objects move in the opposite direction, then their relative speed is equal to the sum of their speeds.

If the speed of boat is x km/hr and the speed of stream is y km/hr, then

speed of boat in upstream = (x – y) km/hr

speed of boat in downstream = (x + y) km/hr

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