Which Average Velocity Formula Should I Use?

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The discussion clarifies two formulas for calculating average velocity: (Vf + Vi)/2 and (Xf - Xi)/Δt. The first formula applies specifically when acceleration is constant, while the second formula is the general definition of average velocity and is always applicable. Users express confusion about when to use each formula, emphasizing the need for context in problem-solving. The conversation highlights the importance of understanding the conditions under which each formula is valid. Ultimately, selecting the correct formula depends on the information provided in the problem.
fightboy
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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.
 
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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.
 
fightboy said:
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.
 
ok that cleared it up, thanks!
 

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