# Need phyeics help (electric charge/Forces)

1. Mar 8, 2009

### austin1250

1. The problem statement, all variables and given/known data

K i need help with like 3 phyics problem on electric forces / charges.

1. One gram of copper has 9.48 10^21 atoms, and each copper atom has 29 electrons.

(a) How many electrons are contained in 1.08 g of copper?
_________ electrons

b. What is the total charge of these electrons?
__________ C

2. Calculate the net charge on a substance consisting of a combination of 7.5 10^13 protons and 4.2 10^13 electrons.
___________ C

3. An alpha particle (charge = +2.0e) is sent at high speed toward a gold nucleus (charge = +79e). What is the electric force acting on the alpha particle when the alpha particle is 4.8 10^-14 m from the gold nucleus?
_______________ N

2. Relevant equations

Elctron -1.6 x 10^-19
Proton: 1.6 x 10^-19
Coulombs Law: Felectric = Kc (q1*q2)/r^2

3. The attempt at a solution

alright iv been having trouble since our teacher did not teach us anything about these barley and the book doesnt help at all.

1st one i dont know where to start.

2nd one i tried just simply adding them together and that didnt work and then i tried using pythagorm theorm because iwas maybe thinking that the net force you need to find like the triange.

3rd one i plugged into the columbs law and i got 6.2x10^38 and i think i got that wrong too?

2. Mar 8, 2009

### austin1250

ight well i actully figured out the last two. but i still can seem to get the 1st one. iv tried all that i can think of can some one help me with that please?

3. Mar 8, 2009

### LowlyPion

For the first one they tell you how many atoms per gram. They tell you how many -e per atom ... where is the problem?

4. Mar 8, 2009

### austin1250

the problem is i get the first part of the question, i do 29 * 9.48e21 then multiply it by 1.08 and get my answer 2.962e23

then how do i find the total charge? do i multiply that by -1.6e-19?

5. Mar 8, 2009

Exactly.