- #1
stunner5000pt
- 1,465
- 4
- Homework Statement
- A spring with spring constant k has an unstretched length of L. A mass m is hung vertically from the spring. The mass is pulled down a distance x and given an initial velocity upward of v.
Determine the maximum length that the spring reaches in terms of the above variables.
Assume the spring has mass zero.
- Relevant Equations
- Conservation of energy
[tex] \Delta E_{k} + \Delta E_{g} + \Delta E_{s} = 0 [/tex]
Included a diagram as well... forgive me... I cannot seem to 'uninvert' the attached picture
final velocity is zero
if we set the lowest point that the mass reaches as zero, then the final height is zero
let H be the 'extra' length that the spring reaches over and above the initial stretch
[tex] \Delta E_{k} + \Delta E_{g} + \Delta E_{s} = 0 [/tex]
[tex] \frac{1}{2} m (v_{2}^2 - v_{1}^2 ) + mg (h_{2} - h_{1}) + \frac{1}{2} k ( (x + h_{f} )^2 - x^2) = 0 [/tex]
using the things that are zero above
[tex] -\frac{1}{2} v^2 - mg h_{f} + \frac{1}{2} k ( (x + h_{f} )^2 - x^2) = 0 [/tex]
[tex] -\frac{1}{2} v^2 - mg h_{f} + \frac{1}{2} k ( 2x h_{f} + h_{f}^2 ) = 0 [/tex]
[tex] \frac{k}{2} h_{f}^2 + h_{x} ( -mg + kx) - \frac{1}{2} v^2 = 0 [/tex]
ok at this point it's getting a bit messy as this requires to go into a quadratic formula but, is this correct so far?
Thank you for help in advance!
final velocity is zero
if we set the lowest point that the mass reaches as zero, then the final height is zero
let H be the 'extra' length that the spring reaches over and above the initial stretch
[tex] \Delta E_{k} + \Delta E_{g} + \Delta E_{s} = 0 [/tex]
[tex] \frac{1}{2} m (v_{2}^2 - v_{1}^2 ) + mg (h_{2} - h_{1}) + \frac{1}{2} k ( (x + h_{f} )^2 - x^2) = 0 [/tex]
using the things that are zero above
[tex] -\frac{1}{2} v^2 - mg h_{f} + \frac{1}{2} k ( (x + h_{f} )^2 - x^2) = 0 [/tex]
[tex] -\frac{1}{2} v^2 - mg h_{f} + \frac{1}{2} k ( 2x h_{f} + h_{f}^2 ) = 0 [/tex]
[tex] \frac{k}{2} h_{f}^2 + h_{x} ( -mg + kx) - \frac{1}{2} v^2 = 0 [/tex]
ok at this point it's getting a bit messy as this requires to go into a quadratic formula but, is this correct so far?
Thank you for help in advance!