How to Calculate Force and Potential in Electrodynamics Exercise?

[castlecharged]

Exercise

A uniform linear distribution of charge of $$\lambda$$ coulombs /meter is situated at a distance r from a point chage Q of opposite sign .

(a) Calculate the force of attraction
(B) show that force is same as if the linear disteibution were replace by a single charge
Q’= 2$$\lambda$$r


can anyone here help me please

thank you for all

 

[issacnewton]

first find the electric field due to the line charge at the location of charge -Q. then you can
find the force...

or you can find the potential at that location and then use the fact that
$\vec E= -\vec \nabla{V}$ since you don't have to worry about
the vector components in the calculation of E above.