Which Average Velocity Formula Should I Use?

[fightboy]

Hey guys I just had a question regarding the equation to calculate average velocity. The first equation I've seen is: Vf+Vi/2, with Vf representing final velocity and Vi representing initial velocity. The second equation I've seen is Xf-Xi/Δt, with X representing position and Δt representing the elapsed time. What is the difference between the two? I get confused on which equation to use for a problem asking for average velocity.

 

[Doc Al]

The first equation, (Vf + Vi)/2, gives the average velocity when the acceleration is constant. It's not true in general.

The second, (Xf - Xi)/Δt, is the definition of average velocity and is always true. Whether it's useful or not depends on what you are given in the problem.

 

[SammyS]

Hey guys I just had a question regarding the equation to calculate average velocity. The first equation I've seen is: Vf+Vi/2, with Vf representing final velocity and Vi representing initial velocity. The second equation I've seen is Xf-Xi/Δt, with X representing position and Δt representing the elapsed time. What is the difference between the two? I get confused on which equation to use for a problem asking for average velocity.

Notice the parentheses Doc Al added in his reply to you.

 

[fightboy]

ok that cleared it up, thanks!

 

[HalfLostAndSearching]

Hello, thank you for your question. The two equations you mentioned are both used to calculate average velocity, but they are derived from different principles.

The first equation, Vf+Vi/2, is known as the average velocity formula and is derived from the definition of average velocity, which is the total displacement divided by the total time. In this equation, Vf represents the final velocity and Vi represents the initial velocity. This equation is often used when the initial and final velocities are known and the time is not specified.

The second equation, Xf-Xi/Δt, is known as the average speed formula and is derived from the definition of average speed, which is the total distance divided by the total time. In this equation, Xf represents the final position and Xi represents the initial position. This equation is often used when the initial and final positions are known and the time is not specified.

The main difference between the two equations is that the first one uses velocities while the second one uses positions. The choice of which equation to use depends on the information given in the problem. If the problem gives velocities, then the first equation should be used. If the problem gives positions, then the second equation should be used.

I hope this helps clarify the difference between the two equations and when to use them. If you have any further questions, please don't hesitate to ask.