Point charge attractioning a positive charge from infinity to 30cm

[goWlfpack]

Homework Statement

A point charge of 2.0 10-9 C is located at the origin. How much work is required to bring a positive charge of 4.0 10-9 C from infinity to the location x = 30.0 cm?

and it requests the answer in J

Homework Equations

W=-q2(delta)V

DeltaV = Ke q1/d

where delta v is potential difference, W is work, q2 and q1 are the charges, Ke is coulombs constant, and d is distance

The Attempt at a Solution

I plugged in all of the variables using 4.0 *10 ^ -9 as my q1 and 2.0*10^-9 as my q2 and that was wrong so i switched them.. again wrong..

 

[Doc Al]

Switching q1 and q2 won't change anything. Show your final expression for the work done and the numbers you plugged in. Is it positive or negative?