jdmarquardt said:
I am confused from the start. I am unsure on how to find the EF for point P without its Charge, and unsure how to approach it.
The word in bold above indicates that you have a misunderstanding. There does
not need to be a charge at point P in order for there to be an electric field there. The electric field you are looking for is the field
due to the other charges. The electric fields of Q
a and Q
b extend throughout space, including to point P. Basically you can think of the electric field as "map" of how an electric charge influences its surroundings. Does that make sense?
You're missing an equation for the electric field of a charge q that tells you how strong it is at a distance r away from that charge. You need to find this equation so that you can use it to compute the strength of charge a and charge b's field at point P.
jdmarquardt said:
Also I am horrible when working to find the spring constant. Any suggestions on how to start, besides a FBD.
Thank you
Since the charges have opposite signs, they are attracted towards each other. However, since they are at opposite ends of the spring, the spring gets compressed as the charges move towards each other. However, as you know, the spring fights back with a restoring force that gets bigger the more you compress the spring. When the outward force from the spring is equal to the inward force from the electric charges, the compression will stop. So, the problem is telling you that, when the spring is compressed down to s = 10 cm, the spring force and the electric force are equal to each other. That means you
know the spring force and you
know the amount of compression. So how would you solve for k?