# A particle inside eletric field

Alois Herzog Heinz
Thread moved from the technical forums, so no HH Template is shown.
Sorry about my english , i'm still learning.

I did it by energy, but i want to solve by integration

QUESTION : A charged and massive particle runs with 66 m/s, 3^10-6 coulomb and 6^10-3 Kg towards a fixed particle with 4,5^10-6 coulomb, separated by 4,3 meters . What's the distance between them which the initial velocity is zero ?

ANSWER : 0,00761 meters .

I started that way :

1) a = F/m ; F= kQq/r² ; 2) v²=vo² - 2.a.d; and i substituted the acceleration gives by 1 in equation 2 . So i isolated d and integrated 4,2 and (4,2-d) interval. It results in a cubic equation which doesn't make sense .

## Answers and Replies

Homework Helper
Hello Alois, This is not a matter of uniform acceleration ! You can't use the SUVAT equations here.
And you don't need to integrate either. That is being taken care of perfectly by using the electric potential.
Or did you do that already and did you find the 8 mm that way ?

Could you show your calculations in a bit more detail ? I can't follow what you mean with (4,2) and (4,2-d) ?

Alois Herzog Heinz
Hello Alois, This is not a matter of uniform acceleration ! You can't use the SUVAT equations here.
And you don't need to integrate either. That is being taken care of perfectly by using the electric potential.
Or did you do that already and did you find the 8 mm that way ?

Could you show your calculations in a bit more detail ? I can't follow what you mean with (4,2) and (4,2-d) ?

I already dit it by using eletric potential and cinetic energy (as Wolfgang Bauer's book did) . By integration i didn't find the correct answer .
I thought even the acceleration is not uniform , is given us how it changes with the distance , and we can evaluate by integrating all points of it in the path . SUVAT equation was the only way i saw to associate velocity , acceleration and distance .

(4,2) and (4,2-d) are the higher and lower integral limits

http://[ATTACH=full]200062[/ATTACH] [ATTACH=full]200063[/ATTACH]

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