# Homework Help: One tough question,find X from graph & equation

1. Dec 2, 2004

### jwalant

i have to do the lab on hooke's law .. i have added the graph & data table to attachment.

1st: Using graph determine the relationship between the F and X, expressing it both as a proportion and an equation. ( I know tht the realtionship is Hooke's law F=KX. But i don't if to use F=KX or f=-kx ?? ) and how do i explain from the graph? ( i know how to find in questions but not in graphs)

2nd: use graph to find X when force is 0N, 8N and 16N.
I am getting for 0 N, X=0 m . For 8N, X= .51m. For 16N i don't know how to find it. Do i just look up in the graph to see where it ends? but then it ends at 13.72N so don't know how to find X for 16 N

3rd: Use equation to find X when force is 0N, 8N and 16N. now, the problem is tht i don't know the K and X . so i can't use F=mg =kx. cauz i don't know k and x. so how do i find both of them? do i use F or X from the graph? i have givin mass so do i use tht?

4th: I have to find Ee, when it is held extended by a 10 N force.. Ok for this i know F=10 N. X=0.64 ( looked from graph if i am right?) now to find Ee I have to find K first right?

so i tried to find using kx=mg .. but now question is that what mass i am goin to use? or do I see the graph at 10N & see X which is 0.64m ? it's confusing cauz it says tht i have to use equation to find it.

i have tried to do these question & have listed the answers of some of them.. but i am not sure if it is right or not. someone plz answer this questions.

thx

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2. Dec 2, 2004

### Gokul43201

Staff Emeritus
The attachment has not yet been approved for viewing, but here's some pointers anyway :

Does the graph have a positive or negative slope ?

You must extrapolate (extend the straight line, or fit a straight line to the data, and extend it) from the graph. Also, you have to know that at 16N you are still in the (elastic) regime where Hooke's Law holds.

You have to determine 'k' from the graph. That tells you what the equation is. This is needed for #1. How do you find the value of 'a' given a graph representing the straight line :
y = ax + b ?

What is Ee, and how is it defined ?

3. Dec 3, 2004

### jwalant

1st one has the graph Postive slope goin in the straight line. {

so for the 2nd on do i look in the graph & figure out wht is the X value at 16 N? oh ok ok I got wht u are saying for 2nd part i got it how to find it.

ok i know how to do 2nd & 3rd but i have problem with 4th

i have to find Ee, which is Ee=o.5 k(x2) . i have Force given. But don't have K & X. my question is tht do i look from the graph & take data of X at 10 N?

IF YESthen i can do rest.