Hi all, I'm currently trying to work out a equation i was given in my physics class and really struggling... Does anyone have any ideas on this for me? I'm not asking for the answer just how on earth to work it out Please Register or Log in to view the hidden image! Is it possible to accelerate an electron in a electric field. If an electric force, of 2x10^-18N acts on the electron (initially at rest) for a time of 1 second, calculate its final velocity. Look up the speed of light and comment on the electrons velocity. I would guess to use Newtons second law of F=ma ? I'm thinking i need to work out acceleration and velocity somehow... Hope you can help Regards Adam Please Register or Log in to view the hidden image!
Just use F=ma and see what your answer is. If your answer is more than about 0.2c then you should not be using Newtonian mechanics but relativity.
Looks like relativity has to come into it, now i am definitely lost!!! I've attempted some research but being honest I'm unsure what to look for. Thanks for the tip about relativity Please Register or Log in to view the hidden image!
Adamh: Have you calculated the acceleration of the electron? Given the acceleration, have you calculated the final velocity, assuming the acceleration is constant? What value did you get?
I suspect that what you are expected to do is to just use F=ma to get a numeric answer, than make a qualitative comment that since the resulting speed is greater than the speed of light, F=ma is the wrong equation to use; it is only accurate at low speeds. I don't think you're supposed to be able to calculate a correct quantitative answer.
So would this work out? F= 2x10^-13N m= 1.9x10^-31 so that would make a= 3.8^-42 m/s ? I think it is just to get a idea that it is faster than the speed of light to prove its false? Thanks for all your replies so far Adam
Multiple mistakes there. Your electron mass is wrong, and you didn't divide the two numbers correctly. F=ma, so a=F/m. Also, you seem to have changed the force from 2x10^-18 N to 2x10^-13 N. Once you've got the acceleration, tell me how you will work out the final speed.
Ahh i see the mistakes, too long on one equation gets to your cells after a while Please Register or Log in to view the hidden image! should be 9.1x10^-31 and i multiplied instead of dividing... should leave me with 2.197^48 now i need to do final speed... Thanks
You seem to be having trouble using a calculator. What is \(2 \times 10^{-18} / 9.1 \times 10^{-31}\)? Hint: it is not \(2.197^{48}\). Not even \(2.197 \times 10^{48}\). What grade are you in at school? Also, so far you've been at this problem for 2 days, and you still don't seem to know how to work out the final speed. If you do all problems this slowly with this number of errors, how will you ever hope to pass the subject?
