(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A uniform electric field exists in the region between two oppositely charged parallel plates (1.64*10^{-2})m apart. A proton is released from rest at the surface of the positively charged plate and strikes the surface of the opposite plate in a time interval (1.60*10^{−6})s.

Find the speed of the proton at the moment it strikes the negatively charged plate.

2. Relevant equations

[tex]x = x_0 + v_0 t + (1/2) a t^2[/tex]

[tex]v = v_0 + a t[/tex]

[tex]v^2 = v_0^2 + 2 a (x - x_0)[/tex]

3. The attempt at a solution

Okay so I found a by using this equation ([tex]x = x_0 + v_0 t + (1/2) a t^2[/tex]) and it came out to be 1.2812*10^10.

To find velocity when it hits, I realized that I get a different answer when I use this ([tex]v = v_0 + a t[/tex]) and that ([tex]v^2 = v_0^2 + 2 a (x - x_0)[/tex]). The correct answer came out when I used the latter equation.

So my question is, why is it that I can't use the first equation? Shouldn't they come out to be the same answer? Did I do something wrong?

Thanks guys.

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# Homework Help: Confused on which equation to use (simple question)

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