Calculate the average speed and average velocity

In summary: It is not difficult to show that the average speed for the round trip is:##\displaystyle \ \text{Average Speed}=\frac{2ab}{a+b} \ . ##This is the harmonic mean for the two speeds.
  • #1
AHashemi
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1. a man drives from a to b with car and speed of 20 km/h and returns from b to a immediately with speed of 30 km/h. what's the average speed and average velocity?

2. V=at+Vi etc

3. I think avg. speed will be 25 km/h and avg. velocity is -10 km/h.
Is that right?

thanks :)
 
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  • #2
See, one thing you need to really understand while doing kinematics in one direction is the difference between distance and displacement., velocity and speed.
One way of not getting fooled by it, the one i used a lot as a beginner is to remember the definition. Now, let's look at average velocity's definition. It means change in displacement in a given amount of time. So, if a person goes from initial point and comes back to it, then what do you think the change in displacement will be?
 
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  • #3
AHashemi said:
1. a man drives from a to b with car and speed of 20 km/h and returns from b to a immediately with speed of 30 km/h. what's the average speed and average velocity?

2. V=at+Vi etc

3. I think avg. speed will be 25 km/h and avg. velocity is -10 km/h.
Is that right?

thanks :)
Hello AHashemi. Welcome to PF .

In addition to what THE BEAST posted:

The definition for average speed is:

##\displaystyle \ \text{Average Speed}=\frac{\text{total distance traveled}}{\text{elapsed time}} \ . ##​

It takes more time to travel from a to b than it does for the return trip. Therefore, the average is not a simple averaging of the two speeds ,

You need to find the total time for the round trip.
 
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FAQ: Calculate the average speed and average velocity

What is the difference between average speed and average velocity?

The average speed is the total distance traveled divided by the total time taken, while average velocity is the displacement divided by the total time taken. Average velocity takes into account the direction of motion, while average speed does not.

How do you calculate average speed and average velocity?

To calculate average speed, divide the total distance traveled by the total time taken. To calculate average velocity, divide the total displacement by the total time taken.

Can average speed and average velocity have different values?

Yes, they can have different values if the object is changing direction during its motion. For example, if an object travels 10 meters north and then 10 meters south in a total time of 10 seconds, its average speed will be 2 m/s, but its average velocity will be 0 m/s since its displacement is 0.

What are the units for average speed and average velocity?

The units for average speed are distance divided by time, such as meters per second or miles per hour. The units for average velocity are displacement divided by time, such as meters per second or miles per hour.

Can average speed and average velocity be negative?

Yes, both average speed and average velocity can be negative if the object is moving in the opposite direction of the reference point. For example, if an object is moving south and the reference point is north, its velocity will be negative.

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