Physics Help Forum Find Electron Velocity

 Jun 13th 2011, 12:59 AM #2 Physics Team     Join Date: Jun 2010 Location: Mauritius Posts: 609 I'm not sure where you're getting your values... anyway, this is how I would have done it: I will first assume that the velocity of the electron is 0 when it is 1000 m away since yo said it 'starts' there. I will not go around using the basic equations of motion since the acceleration is not constant. The force acting on the electron varies as the distance varies and this will be a real pain to find the acceleration at each and every point in between the points you want to get the velocity. Instead, it's easier to go around energy equations. Potential energy 1000 m away from the proton: $V = \frac{q}{4\pi\epsilon_or}$ Using the values that we have: $V = \frac{1}{4,000\pi\epsilon_o}$ Now, at 100 m; $V = \frac{1}{400\pi\epsilon_o}$ And so on. The velocity at 100 m is given by the kinetic energy formula and the change in potential energy. Lost in PE = Gain in KE $\frac{1}{400\pi\epsilon_o} - \frac{1}{4000\pi\epsilon_o} = \frac12 mv^2$ You solve for v. To get the velocity at 10 m, you use: http://latex.codecogs.com/gif.latex?...\frac12%20mv^2 (the site wouldn't let me post a 5th image... -.-" ) And so on. I hope it helped! PS: Eo [ Epsilon nought is the permittivity of free space and is a very small value. There are some schools which teack V = kq/r though, where k = 1/(4pi Eo) ] __________________ Jerry (Got my results!) It is easier to protect your feet with slippers than to cover the earth with carpet. No one can go back and change a bad beginning; but anyone can start now and create a successful ending. If a problem can be solved, no need to worry about it. If it cannot be solved what is the use of worrying?