# Finding the spring constant while stretching and compressing

#### Eric0

1. The problem statement, all variables and given/known data
I have a physics lab that I'm just not making any progress on. For this lab my group used a 314 g cart. Two springs were used, both attached to the cart, and one being stretched the other compressed. The cart was then ran horizontally and it's velocity was found.

I want to find the the spring constant for each trial and then average it. I have the velocities for each trial of the cart after stretching/compressing. The three velocities of the cart after being attached to the stretched or compressed string in m/s are 1.18, 2.68, and 3.65. For the compression trials the velocity in m/s was found to be .2, .7, and 1.0.

Natural length of the stretched spring is 6 cm and the compressed 8.4 cm.

2. Relevant equations

3. The attempt at a solution

I tried to used the formula given: k= (1/2mv2)/x with x being the distance stretched/compressed. The values I got were kind of funky. I'm thinking I need to use kinetic or potential energy here.

#### The Liberator

I tried to used the formula given: k= (1/2mv2)/x with x being the distance stretched/compressed. The values I got were kind of funky. I'm thinking I need to use kinetic or potential energy here.
Hi Eric,

I think that I might be very wrong here, but I am looking at one of the more basic spring equations here; elastic potential energy: Us = 1/2kx2

…And if it is re-arranged, I cannot find that it turns into one of the equations that you are using here. I might very well be wrong, and I am sure that someone else will be able to help you properly, but I think you need to check you equations and re look at it in a different way.

Liberator.

### The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving