A balloon rubbed against denim gains a

charge of −2.0 µC.
What is the electric force between the
balloon and the denim when the two are
separated by a distance of 5.0 cm? (Assume that the charges are located at a
point.) The value of the Coulomb constant is
8.98755 × 10
9
N · m2
/C
2
.
Answer in units of N

5 answers

F=kQ^2/r^2 =
=8.98755•10^9•(210^-6)^2/0.05^2 = 14.4 N
It says its wrong.
Where did you get 210?
If the balloon gains a charge of -2.0 μC, the denim has to gain a charge of +2.0 μC.
May be they want
F=k•Q1•Q2/r^2 =
=8.98755•10^9•(2•10^-6) •(-2•10^-6) /(0.05)^2 = - 14.4 N
cell