Coulomb's Law/Newton's Law of Universal Gravitation (Precalculus?)

1. Jul 9, 2013

Bill Nye Tho

1. The problem statement, all variables and given/known data
The electric field, E, a distance D away from a charged particle is directly proportional to the size of the charge Q, and inversely proportional to the square of the distance D. If the charge is increased by 40% and the distance is increased by 30%, by what percentage does the electric field change?

2. Relevant equations

???

3. The attempt at a solution

I'm actually pretty upset with how rusty I am at this but for some reason when I read these problems (and precalculus gravitational problems), I can't seem to get Classical Mechanics and Electromagnetism equations out of my mind. Although, I know that the answer will pretty much apply Coulomb's Law. Maybe I'm overthinking this..

ED = Q = 1/D^2

+.35(Q)
+.2(D)

Is all I'm interpreting from the question.

2. Jul 9, 2013

SteamKing

Staff Emeritus
What do +.35(Q) and +.2(D) mean?

3. Jul 9, 2013

Bill Nye Tho

Ah, I'm sorry.

I meant to write +.4Q and +.3D.

I'm increasing the charge by 40% and the distance by 30%

4. Jul 9, 2013

Dick

If you increase Q by 40% then Q becomes 1.4Q. The original electric field is E=kQ/D^2. Compute the ratio of the new field to the original field.

5. Jul 9, 2013

Bill Nye Tho

I know that, I'm just separating the added charge and added distance from the setup because I'm not even sure if I have that done correctly.

6. Jul 9, 2013

Dick

That you understand it would be pretty hard to tell when you write things like +.35(Q) and +.2(D). If you know the ratio of initial and final charges and distance then use Coulomb's formula to compute the ratio of electric fields. This is pretty straightforward.

7. Jul 9, 2013

Bill Nye Tho

I think I figured it out, with your help. Thanks