# Hard potential energy function question

1. Oct 17, 2011

### Lucy Yeats

1. The problem statement, all variables and given/known data
Potential energy function A particle of mass m, starting from x = −∞, approaches
a force region whose potential is given by
V (x) =(ka^2)/((x^2)+(a^2))
where V0 > 0 and a are constants.
(a) Derive an expression for the force on the particle as a function of

2. Relevant equations

E=F/Q, V=W/Q, E=V/d

3. The attempt at a solution

I tried to substitute it into the equations above, but it didn't work. A friend thought the answer involved calculus, but I'm not sure where to start. Any hints would be much appreciated...

2. Oct 17, 2011

### Lucy Yeats

Is it correct that potential x mass = potential energy?

3. Oct 17, 2011

### Lucy Yeats

Do I need to introduce a constant for the charge, of can I express F without this? Help, please! Thanks! :-)

4. Oct 17, 2011

### SammyS

Staff Emeritus
No.

5. Oct 17, 2011

### SammyS

Staff Emeritus
You don't need the charge.

You can express F without introducing a charge.

Do you know how to take the gradient?

F = - V .

Otherwise, F = - dV(x)/dx .

6. Oct 17, 2011

:-)