How Much Charge Does the Second Charge Have?

[dminus]

Homework Statement

Two charges, one at the origin and one at x=1.6 m produce a field 1.59x10^3N/C at x = 9.11 m. The charge at the origin has a charge of 1.11 x 10^-5 C. How much charge does the second charge have?

http://books.google.com/books?id=vN...the origin has a magnitude of 845 N/C&f=false

Page 96 Question 3.49

Homework Equations

E=F/q
E=kq1q2/r^2
k=8.99x10^9

The Attempt at a Solution

I tried using coulomb's law to find Q2

1590=(9x10^9)(1.11x10^-5)(q2)/(9.11^2)

But my solution did not match the answer which was q2 = 2.44x10^-6C

 

[vela]

That's not the correct equation for the electric field due to a point charge. You have the equation for the force between two point charges. It's not really useful for this problem.

 

[dminus]

ah yes i got it ty