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Now, we have the quantity which define how fast is the position changing with time.

Average Velocity: It is defined as the change in displacement or position divided by the time elapsed or the time interval. Let us consider the final position is xf , initial position xi, the displacement Δx (delta x) and time interval Δt.

So that, Average velocity = Change in displacement/change in time

Average speed: It is defined as the total distance travelled divided by the time elapsed or the time interval. Let us consider the distance travelled is d and time interval Δt.

So that, Average velocity = Total distance travelled/ change in time

Let’s we have an example:

Example:- Suppose a car is moving along a straight line as given in the figure. Car moves from A to C in 10 sec and returns from C to B in 5 sec.

(a) What are the average velocity and average speed of the car in going from A to C?

Answer:- Average velocity = Displace/time interval = 50/10 = 5 m/s

Average speed = Total distance/ time interval = 50/10 = 5 m/s

In this case both average velocity and average speed is equal in magnitude.

(b) What are the average velocity and average speed of the car in going A to C and back to B?

Answer:- Average velocity = Displacement/time interval = 30/(10+5) = 30/15 = 2 m/s

Average speed = Total distance/ time interval = (50+20)/(10+5) = 70/15 = 4.66 m/s.