Average Speed and Average Velocity

Physics

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Average speed

Average speed is defined as the total distance travelled by the body in total time i.e.

It is a scalar quantity. Its unit is m/s.

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Average velocity


It is a vector quantity and has units of m/s.
Magnitude of average velocity is always less than or equal to the average speed because displacement is always smaller than or equal to distance.

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Calculating average speed

Average speed is found by first finding the total distance covered by the object and dividing it by the total time taken in travelling the distance.
Example:
A boy covers a circle of radius m in s.
The total distance covered by him will be  
Average speed will be

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Non-Uniform Speed and Velocity

Non-Uniform Speed : When a body covers unequal distances in equal intervals of time, then that body is said to be in non uniform speed.
For e.g., an object thrown into air, like stone, moves at non-uniform speed, lift used to go up or down in a building.
Non-Uniform Velocity : When the velocity is not uniform i.e. not constant. This implies that the velocity of the object moving with non uniform velocity is either increasing or decreasing with time i.e. the object is accelerating or decelerating.
Since velocity is a vector quantity, hence it depends on two factors namely speed and direction
If any of the two will change, velocity will also get changed.
So, we can say that the object is moving with non uniform velocity, if an object is :
1. changing speed wrt time but in the same direction.
2. changing direction wrt time while moving with constant speed.( e.g., motion of a particle in a circular path with constant speed)
3. changing both speed and direction wrt time.

REVISE WITH CONCEPTS

Instantaneous Velocity and Instantaneous Speed

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Velocity - Time Graph

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Important Questions

A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is : 

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A man walks on a straight road from his home to a market  away with a speed of . Finding the market closed, he instantly turns and walks back home with a speed of . What is the
(a) magnitude of average velocity, and
(b) average speed of the man over the interval of time
(i)  to ,
(ii)  to  
(iii)  to

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The position of an object moving along x-axis is given by x = a + , where a = 8.5 m and b = 2.5 m and t is measured in seconds. The average velocity of the object between t = 2 s and t = 4 s is

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A car travels from A to B at a, speed of and returns at a speed of . The average speed of the car for the whole journey is:

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A car travels the first one third of a certain distance with a speed of 10 km/hr, the next one third with a speed of 20 km/hr and the last one third distance with a speed of 60 km/hr The average speed of the car for the whole journey is

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A car covers the first half the distance  between two places at 40 km/h another half at 60 km/h, the average speed of car

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An artificial satellite is moving in a circular orbit of radius 42250 km. Calculate its speed if it takes 24 hours to revolve around the earth.

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A particle moving in a straight line covers half the distance with speed of . The other half of the distance is covered in two equal time interval with speed of and respectively. The average speed of the particle during this motion is 

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Joseph Jogs from one end  to the other end  of a straight  road in  minutes  seconds and then turns around and jogs  back to point  in another  minute. What are Joseph's average speeds and velocities in jogging (a) from  to  and (b) from  to ?

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A motorcyclist drives from A to B with a uniform speed of and returns with a speed of . Find the average speed.

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