# Homework Help: Coulomb's Law

1. Jan 14, 2006

### Punchlinegirl

A particle of mass 63 g and charge 59 $$\mu C$$ is released from rest when it is 71 cm from a second particle of charge -27 $$\mu C$$. Determine the magnitude of the initial acceleration of the 63 g particle. Answer in units of m/s^2.

I used Coulomb's Law, F= $$1/4\pi \epsilon_o * (5.9 x10^-6 * -2.7 x 10^-6) / .71^2$$
I know that E_o = 8.85 x 10^-12.
Solving this gave me .284.
Then I set it equal to ma.
63 a = .284
Solving for a gave me .00451 m/s^2.
Can someone tell me what I'm doing wrong?

2. Jan 14, 2006

### Astronuc

Staff Emeritus
Make sure the units are correct. If the force is in N, which it appears to be, then the mass must be in kg (0.063 kg = 63 g).

Perhaps it would be helpful to keep a chart of cgs and mks units available.

3. Jan 14, 2006

### Punchlinegirl

so if the rest of my setup is right, I get .063a= .284.
Solving for a gives me 4.51 m/s^2, which still isn't right.
Am I doing something else wrong?

4. Jan 14, 2006

### lightgrav

59 microCoulombs = 59.E-6 C , not 5.9E-6 C
same for the 27 uC .