# Homework Help: Quick Question about the acceleration formula

1. Apr 17, 2006

### oooo

When you use the formula a=F*k, what are the units of k (such as N, m, s, that kind of thing). I need to know for a problem I have to do for homework, so if you could clear it up for me it would help!

2. Apr 17, 2006

### Pseudo Statistic

Think about it this way, a is ms^-2, and F is N. By the definition of 1 N, 1 N = 1 kg ms^-2
So,
ms^-2 = (X)* kg ms^-2
Where X is the unknown unit of k.......
In this case, treat each unit as an algebraic quantity, re-arrange for X and you'll know what the units are... (Dimensional analysis...)

You may ask why I left the numbers out..... Well, even if you have 3 N on one side with a being 1 ms^-2 on the other side, we really don't care what the value of k IS in this case, just what kind of a unit it represents...
So yeah.

3. Apr 17, 2006

### oooo

Well, all that I know is that in Newton's Second Law, F=m*a, which is the same as a=F/m. Then, looking at a similar formula using k, I see that a=k/m. Thus I thought that k=F and thus k was in units of Newtons. But, for some reason I was wrong. Am I on the right track???

4. Apr 17, 2006

### Pseudo Statistic

Actually, I think you're referring to "Hooke's Law".
In that case, F = kx... = ma, or a = kx/m... not k/m....

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