## Probing potential (Physics help)

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Mon Aug 23, 2010 3:47 am
Squall says...

If there are anyone there that does physics or whatnot, then I greatly appreciate your help on a question that I'm stuck on lol.

Question: The electric potential V in a region of space is given as:

V(x) = Ax^2 + Bx

where V is in Volts and x is in metres.

There is a zero electric potential at the point X0 = -0.45 m. Furthermore when a test charge Q0 = -3.60*10^-6 C moves in this field from the point X1 = 1.85 m to the origin, it does 3.50*10^-5 joules of work.

Determine the values of the constants A and B and their correct SI units.

The answer says A is 2.285 and B is 5.0, but I want to know how to get to the answer.

Thanks.

Andy.
"To the edge of the universe and back. Endure and survive."

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Mon Aug 23, 2010 6:52 am
Snoink says...

I haven't actually plugged in the numbers, but we know that:

dW = qo*E

and we know that

Vf - Vi = - Integral(E•ds)

We have Vf - Vi, W, and qo, so plug that in. We should get an expression with A and B.

Also, we know that:

V(-0.45) = 0

Which means we have two different equations with A and B in it. Use substitution or a matrix to solve for A and B. You should get those numbers.
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