Magnitude of the Net Electrostatic Force On an Oxygen Atom

[shimizua]

Homework Statement

The water molecule forms an angle, with hydrogen atoms at the tips and the oxygen atom at the vertex (see diagram in the previous problem).
Assume that the angle at the oxygen atom is Θ = 103.5o and the distance between the oxygen and the hydrogen atoms is d = 93.1 x 10-9 m.
Calculate the magnitude of the net electrostatic force on the oxygen atom. Use the charges from the previous problem.

This next stuff is what i have already figured out in a different problem that they want you to use in this one.
The water molecule consists of two hydrogen atoms and one oxygen atom. Since the oxygen atom has a higher electronegativity than the hydrogen atom, the side of the molecule with the oxygen atom has a partial negative charge. Assume that the partial negative charge on the oxygen atom is Q1 = -1.104 x 10-19 C. What is the magnitude of the charge Q2 on each hydrogen atom?

and here is the picture.
http://jilawww.colorado.edu/beckergroup/figures/Water.jpg
For this part i got an answer of 5.52e-20 C which the computer said was correct.
that should be all the info you need

Homework Equations

so i am pretty sure that you do F=(k*q1*q2)/r^2 but i am just unsure of why they give you the angle of the oxygen to the hydrogen and what to do with it. please help me!

The Attempt at a Solution

well k is a constant that is 9*10^9 (i think) q2 is the 5.52e-20 C that i found inthe other equation, i am trying to find q1 and r 1/2(93.1x10^-9) but other then that i have no idea what to do.

 

[Carid]

Isn't the question asking you for the vector sum of the two electrostatic forces on the oxygen atom due to the two hydrogen atoms?