1. ## Vectors

Electric point charges of magnitude 3,5 and 7 are placed at the points P(1,2,3) Q(2,3,4) and R(3,4,5) respectively. What is the magnitude and direction of the resultant force on a unit point charge placed at the point P(1,1,1)?. ( You may assume a single constant k to include electrical properties)

2. ## Re: Vectors

How far along are you? It might be difficult to draw a diagram of the problem because it is 3 dimensional, but you could start by setting up the vector sum:

$\overrightarrow F_{net}=\overrightarrow F_P+\overrightarrow F_Q+\overrightarrow F_R$

So you need to find each vector by finding the component of each vector. Have you tried this?

3. ## Re: Vectors

Yeah I have tried that. As we know the directions along which the forces act, I got the unit vector along each 3 directions and multiplied it by the magnitude of the force in order to get the 3 forces in vector form. And I think the resultant is the addition of the 3 vectors. But I'm having a confusion because they have included a 'k' saying "You may assume a single constant k to include electrical properties". How does this come into the answer?
Any help would be great.

4. ## Re: Vectors

?? If a charge, of magnitude 1, is at distance 1 from a charge of magnitude 2, what is the force between them? If you cannot answer that, how could you hope to answer the given question?

5. ## Re: Vectors

Please see whether I got that right this time.
Electrostatic force between 2 particles is k(Q1Q2)/ r^2 .

So, I can get the magnitudes of the forces by this as I know the magnitudes of the charges and the distance between them. Then I can get the unit vectors along the directions on which these forces act and multiply them by the force which I got from the equation above to get it in vector form. Then I can add the 3 vectors to get the resultant.

6. ## Re: Vectors

Originally Posted by Kristen111111111111111111
Please see whether I got that right this time.
Electrostatic force between 2 particles is k(Q1Q2)/ r^2 .
Yes, that's true (well, that the magnitude of the force vector- I assume that's what you meant). That's where the "k" came in!

So, I can get the magnitudes of the forces by this as I know the magnitudes of the charges and the distance between them. Then I can get the unit vectors along the directions on which these forces act and multiply them by the force which I got from the equation above to get it in vector form. Then I can add the 3 vectors to get the resultant.
Yes, that will work.