HELP with Charges

1. Jan 23, 2012

gotpink74

1. The problem statement, all variables and given/known data
What is the electric force between a glass ball that has +2.8 µC of charge and a rubber ball that has -4.8 µC of charge when they are separated by a distance of 4.5 cm?

2. Relevant equations

F=k*Q1*Q2/r^2

3. The attempt at a solution
-59.6507
-8.8888888.889
4.4380e12

2. Jan 23, 2012

gotpink74

is K 9*10^9

3. Jan 23, 2012

iRaid

Yes.

4. Jan 23, 2012

gotpink74

i got -59.7333 but it is still wrong i do not know what i am doing wrong

5. Jan 23, 2012

Redbelly98

Staff Emeritus

6. Jan 23, 2012

gotpink74

(9*10^9)*(2.8*10^(-6))*(-4.8*10^(-6))/0.045^2

7. Jan 23, 2012

Crwth

Are you using UTexas Quest? If so, does it give you a value for k? The rounding difference might make your answer a bit off.

8. Jan 23, 2012

Redbelly98

Staff Emeritus
Usually they just want the magnitude of the force for this type of question. Try without the minus sign, otherwise it looks good to me. You should probably not go more precise than 3 significant figures too.