arildno said:That is correct, as long as you remember that the implied direction is AWAY from Q4.
On vector form, we have:
[tex]\vec{F}_{41}=\frac{1}{4\pi\epsilon_{0}}\frac{Q_{1}Q_{4}}{r_{41}^{2}}\frac{\vec{r}_{4}-\vec{r}_{1}}{r_{41}}[/tex]
EXPLANATIONS:
1)Here, I have included the last fraction to have the basic direction explicitly included.
2)[tex]\vec{F}_{41}[/tex] means: The force acting on Q4 from Q1
3) [tex]r_{41}[/tex] is the DISTANCE between Q1 and Q4, that is, some positive number.
CALCULATIONS:
Q1=2.0 nC
Q4=5.0 nC
Hence, [tex]Q1*Q4=10.0(nC)^{2}[/tex]
[tex]\vec{r}_{4}=\vec{0}[/tex] (that is, situated at the origin)
[tex]\vec{r}_{1}= 0.05m\vec{i}[/tex]
(that is, situated 0.05m to the right-hand side of Q4 at the origin)
Hence, [tex]\vec{r}_{4}-\vec{r}_{1}=-0.05m\vec{i}[/tex]
That is, the direction indicated by this quantity is leftwards.
[tex]r_{41}=0.05m[/tex] that is the DISTANCE between Q1 and Q4 is 0.05m
Collecting all together, we have:
[tex]\vec{F}_{41}=-\frac{1}{4\pi\epsilon_{0}}\frac{10.0(nC)^{2}}{(0.05m)^{2}}\vec{i}[/tex]
That is, the force on Q4 from Q1 is directed leftwards.
Q4 tends to be REPELLED from Q1, because they have EQUAL TYPE OF CHARGE!
Was this okay?
I chose not to pick on that, because I sensed there were more pressing issues at hand.suf7 said:isnt my calculation incorrect because i never put the "-" in front of the 0.05??
so that makes the direction negative right?