# Calculating the closest possible distance of approach

1. Jan 3, 2010

### rreedde

1. The problem statement, all variables and given/known data
An alpha particle 4 2 He 2+ approaches a stationary gold nucleus 197 79 Au at a speed of 7.0 X 10^6 ms-1.
By considering only electrostatic repulsion, calculate the closest possible distance of apporach between the alpha particle and gold nucleus.

2. Relevant equations
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3. The attempt at a solution
Charge of Helium particle = 2e
Charge of gold nucleus = 79 e
And im just stuck here, how do i use the value of the speed of the particle in my working?

2. Jan 3, 2010

### diazona

Try thinking about it in terms of energy.

3. Jan 3, 2010

### Winzer

I agree with this.
The alpha particle stars of with a speed and thus a certain type of energy(hint).
When the particle reaches its closest approach, all the energy is converted into this other type of energy. You should be able to get it from there.

4. May 7, 2011

### planauts

Is the answer to this problem 2.2165 * 10^-13 m?