# A mass spring system

1. Jun 3, 2007

### dirkwbint

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

http://img174.imageshack.us/img174/364/favt1ot7.jpg [Broken]

2. Relevant equations

a energy balance and a F=ma in z-direction

3. The attempt at a solution
I will neglect D (is that reasonable?) Use an energy and force balance:

$$\frac{1}{2} k (\sqrt{(w/2)^2 + h^2} - L0 )^2 = mg\Delta H + D\Delta H,\ H=h+w/2.....eq1$$

$$3.8mg= 2cos( \alpha)* k * ( \sqrt{ (w/2)^2 + (w/2)^2} - L{0} )$$

$$with\ \alpha = arccos( (w/2) / ( \sqrt{ (w/2)^2 + (w/2)^2 }...... eq2$$

2 eq's with 2 unknowns => L0 and k

solve it leads to complex L0 and k! What am I doing wrong?

Last edited by a moderator: May 2, 2017