Need phyeics help (electric charge/Forces)

Homework Statement

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

Homework Equations

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

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?

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?

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

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

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?

CompuChip