How Do You Calculate Electric Forces and Fields in AP Physics Problems?

[se1zure]

Hi, my name is Cory. I need a little help with one of my AP physics assignments, dealing with Electric Charge, Forces and Fields.

I got most of the problems, however here are a few I could use some help / be walked through on.

Problem 36)
On average, the electron and proton in a hydrogen atom are separated by a distance of (5.3 x 10 -11 m), assuming the orbit of the electron to be circular,
(a) what is the electric force on the electron? and (b) WHat is the electrons orbital speed? and (c) What is teh magnitude of the electrons entripetal acceleration in units of (g).
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I'm guessing I need to use fe = kqq
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r^2
however, I'm not sure where rotational comes into play, nor how to do the rotational portion.
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Problem 55)
What would be the magnitude and the direction of a vertical electric field that would just support the weight of a proton on the surface of the Earth? of an Electron?


and lastly,

Problem 61)
What is the electric field at the center of the sqaure in the following figure:

 

[Decan]

For problem 36, you do need to use the equation listed to figure out the force on the electron for part a. Once you have the force, how can you relate that to the electrons speed and acceleration?