Question

(a) Two point charges totaling 7.00 µC exert a repulsive force of 0.200 N on one another when separated by 0.215 m. What is the charge on each?
smallest charge
Incorrect: Your answer is incorrect. µC
largest charge
Incorrect: Your answer is incorrect. µC

(b) What is the charge on each if the force is attractive?
smallest charge
µC
largest charge
µC

Answer 1

suppose the charges are q1 and q2
the question tells you the value of q1 + q2
also, knowing the force between them, you can use coulombs law to calculate q1*q2
you then have 2 equations for your 2 unknowns, q1 and q2

Answer 2

can you show me the formula revised to figure it out

Answer 3

do you know coulombs law for the force between two charges ?

Answer 4

i know f=kq1g2/r^2

Answer 5

then its a quadratic right?

Answer 6

yes, you do end up with a quadratic for the values of the charge

Answer 7

q1^2-q1(-7E-6)+(21.5E-11)=0 ?

Answer 8

you're close but it's not quite what I have

Answer 9

\[q1+q2=7*10^{-6}\]

Answer 10

\[q1*q2=1.027*10^{-12}\]

Answer 11

im getting lost in the algebra
substitute q1 or 2 for a and solve right?

Answer 12

try working through it without numbers first, so say q1 + q2 = m and q1*q2 = n

Answer 13

so q2 = n/q1

Answer 14

then substitute for q2 in the first expression to get q1 +n/q1 =m

Answer 15

multiply through by q1 to get q1^2 +n = m*q1

Answer 16

rearrange to get q1^2 - m*q1 + n = 0

Answer 17

then the solutions are \[\frac{ 1 }{ 2}[m \pm \sqrt{m^2-4*n}]\]

Answer 18

plug in the values, \[m=7*10^{-6}\] and \[n=1.027*10^{-12}\]

Answer 19

let me know what you get for the two solutions

Answer 20

6.82 and1.027

Answer 21

well i have 6.85 for one value

Answer 22

do your two values add up to 7 like they're supposed to ?

Answer 23

i was * to make 7

Answer 24

.18

Answer 25

ok, if you try 6.82 and o.18, what do they give for the product q1*q2 ?

Answer 26

when i enter my answers it tells me 6.82 is correct for the large charge but 0.18 is wrong for the smaller

Answer 27

the correct answers are 6.85 and 0.15, you've probably made a slight error with the numbers somewhere

Answer 28

microcoulombs, of course

Answer 29

yes the the -6

Answer 30

q1*q2 has to come to 1.027 *10-12 and q1+q2 has to come to 7*10-6

Answer 31

it accepted .15 wth strange

Answer 32

and the 6.82

Answer 33

i thought they should have equaled 7 but

Answer 34

the main thing is to understand the method, you might want to check your numerical calculation to see if there was a slight error somewhere

Answer 35

yes they do have to equal 7, the larger charge is 6.85

Answer 36

thanks for spending so much time with me

Answer 37

no problem

Answer 38

so now i do the same but with opp charge right

Answer 39

what about the attractive force
?

Answer 40

use the numbers i just got?

Answer 41

the question states that the force is repulsive, you have the two values of the charges, there is no more to be done, you've solved the problem

Answer 42

there is a part b asking the charge on force is attractive

Answer 43

but thats cool i dont wanna bug ya i appreciate what youve helped me with