# Oscillation Question

1. Nov 23, 2006

### cd80187

The suspension system of a 1700 kg automobile "sags" 13 cm when the chassis is placed on it. Also, the oscillation amplitude decreases by 43% each cycle. Estimate the values of (a) the spring constant k and (b) the damping constant b for the spring and shock absorber system of one wheel, assuming each wheel supports 425 kg.

I have looked at this problem for awhile, and I have no clue where to even start... So I was just looking for a little help to get started in the right place, thank you in advance

2. Nov 23, 2006

### Hootenanny

Staff Emeritus
HINT: Hooke's Law

3. Nov 25, 2006

### MT1986

Alright, I have the same question. After applying Hooke's Law I think i found the spring constant, which is fairly straightforward. Now, how do i find the damping constant? I'm a little unclear as to which equation to use, because they have more then one unknown variable.

4. Nov 27, 2006

### cd80187

I was able to solve the first part, but I could not get the second part. The book gives us two equations, and I think I am supposed to use this one : omega (w) = Square root of (k/m - b squared/4msquared). But beyond that, I am unsure what I am supposed to do

5. Nov 27, 2006

### Hootenanny

Staff Emeritus
I think that the following equation may be more useful.

$$x(t)=x_m\cdot e^{-bt/2m}\cos(\omega\cdot t)$$

where x is the displacement, xm is the amplitude, and I'm sure you know the rest...

Now, from the above equation we can see that at t = 0 $x=x_m$, yes? If we then assume that $b<<\sqrt{km}$, then the period of the springs is approximately that of an undamped mass-spring system, therefore we can calculate the time period of the oscillator. And you know that after one time period that xm has decrease by 43%. Can you go from here?

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