# Homework Help: Uniform circlur motion

1. Oct 7, 2007

### veloix

1. The problem statement, all variables and given/known data
In the Bohr model of the hydrogen atom, the speed of the electron is approximately 2.00 x 10^6 m/s.
(a) Find the force acting on the electron as it revolves in a circular orbit of radius 5.50x 10^-11 m

2. Relevant equations

∑fy=ma=mv^2/r
ac=v^2/r

3. The attempt at a solution

i am always magnitude orders off for the force and dont know why, when do free body the only force i can think of that acts on the electron is the centripcal accleration due it a ciclulr orbrit. looking in the book the mass of a hydrogen atom is 1.67x10^-27.
∑fy= (1.67x10^-27)(2x10^6)^2/(5.50x10^-11)
= 1.21x10-4 N but this wrong can some help me understand this better.

2. Oct 7, 2007

### PhanthomJay

You are incorrectly using the mass of the atom. What mass should you be using?

3. Oct 7, 2007

atomic mass
?

4. Oct 7, 2007

### veloix

ah the mass of the electron

5. Oct 7, 2007

### PhanthomJay

yes..........!

6. Oct 7, 2007

### veloix

but i still get the wrong answer.

7. Oct 7, 2007

### veloix

fy=mv^2/r+mg
Fy=(9.108*10^-31)(2*10^6)^2/(5.5*10^-11)+(9.108*10^-31)(9.80)
= 6.6*10^-8
still off by magnitudes i dont what to do

8. Oct 8, 2007

### PhanthomJay

The centripetal force is primarily delivered by the electromagnetic force between the positively charged proton and negatively charged electron. But no matter what the source is for the force, what's the formula for centripetal force?