How to Calculate the Elongation of a Spring with a Submerged Block?

[dban33]

Homework Statement

One end of a massless spring with hook-law constant K=119 N/M is epoxied to the bottom of a beaker. The other end of the spring is epoxied to a wooden block of mass m=4.17 kg and density 695 kg/m^3. THe beaker if filled with water until the block is fully immersed. Calculate the elongation of the spring. delta L= ??

Homework Equations

The equation I was trying to use was Fx=-kx
I do not think this is correct because my answer was wrong.

The Attempt at a Solution

I put the data into the equation -k as -119 and x as 4.17 times 695 but in the end I still did not get delta L and that is what I need. I do not know where to begin with this problem.

 

[tiny-tim]

… The other end of the spring is epoxied to a wooden block of mass m=4.17 kg and density 695 kg/m^3. THe beaker if filled with water until the block is fully immersed. Calculate the elongation of the spring. delta L= ??
…
I put the data into the equation … x as 4.17 times 695 …

Hi dban33!

You've calculated the force by multiplying by the density …

but the lighter the block is, the stronger the force will be …

so you should multiply by … ?

 

[dban33]

Ok...so the lighter the block is...the stronger the force will be. Does that mean that for the equation F=-kx...im trying to solve for x right? because x is the elongation of the spring. This would mean that I would have to know the force of the block. Is the force of an object its mass times gravitational force?? F=mg?

 

[tiny-tim]

hmm … you'd better look at http://en.wikipedia.org/wiki/Buoyancy