Calculate the speed of a particle?

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The discussion revolves around calculating the speed of an electron moving from point A to point B in an electrostatic field. It is established that the electron has more potential energy at point A than at point B, indicating it moves faster at point B. Participants express confusion about the concept of negative work and how it relates to changes in kinetic energy. Clarifications are provided that negative kinetic energy indicates a decrease in speed, not an impossibility in calculation. The key takeaway is that the speed at point A is indeed less than at point B, aligning with the principles of energy conservation.
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Homework Statement


If you have an electron in the following electrostatic field:

------------------------- (+)
(-) B 2m from origin(-) A 1m from origin

------------------------- (-) Origin

Okay, so; the force field is pushing the electron from point A to point B.

It has more potential energy at point A than point B, meaning point B is moving faster than point A.

So I have to find the velocity of the electron at point A assuming that its HALF of the speed at point B

Homework Equations


F = kq1q2 / r^2
E = kq1q2 / r

Ek = 1/2 m v^2
Et1 = Ek + Ep
Et1 = Et2

The Attempt at a Solution


If we move an electron from point A to point B, we do negative work on it. How is this possible? I don't understand this at all.

Also, if it gains 10 J of potential energy from point B to A, and we have to calculate its speed.. How is this possible?

We have the equation

Ek ---> transfer to ----> Ep

So our change in kinetic energy is now negative.

But we can't take the square root of a negative value, so we can't solve for velocity
 
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x86 said:
If we move an electron from point A to point B, we do negative work on it. How is this possible? I don't understand this at all.
Who is this "we" that you speak of?
You have worked out that the electron has negative work done on it - by what?

If you physically pushed the electron from B to A, you would have to do positive work on it right?

Also, if it gains 10 J of potential energy from point B to A, and we have to calculate its speed.. How is this possible?
How about doing it the other way around?

Note - the negative KE is a negative change in KE.
It just means you end up with less than you started - which is find because you know that the speed at A is less than the speed at B.
 
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