# Spring Mass Problem

1. Nov 16, 2009

### DrMath

1. The problem statement, all variables and given/known data

Hi PF frens,
I've got the attached picture translated into differential equation representation.
However, not so sure how the r(t) and f multiply dee-y / dee-t comes about.

2. Relevant equations

3. The attempt at a solution

see attached jpeg.

#### Attached Files:

• ###### Spring-Mass.JPG
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2. Nov 16, 2009

### fatra2

Hi there,

From what I can see, the $$f \frac{dy}{dt}$$ seems to be the friction force applied on the system. I would guess r(t) the simple gravitational pull, but I might be mistaking.

Cheers