Young Writers Society

Home » Forums » Community » Lounge, The » Homework Help

Probing potential (Physics help)

User avatar
672 Reviews

Gender: Male
Points: 5577
Reviews: 672
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.


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

User avatar
3729 Reviews


Gender: Female
Points: 1009
Reviews: 3729
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.
Ubi caritas est vera, Deus ibi est.

"The mark of your ignorance is the depth of your belief in injustice and tragedy. What the caterpillar calls the end of the world, the Master calls the butterfly." ~ Richard Bach

Moth and Myth <- My comic! :D

It does not do to dwell on dreams and forget to live.
— Albus Dumbledore