Plotting Length of Spring vs Load: Find Unloaded Length & Extension

[Taylor_1989]

Homework Statement

The following results were obtained when a spring was stretched:
Load/N: 1.0 3.0 4.5 6.0 7.5
Length of spring/cm:12.0 15.5 19.0 22.0 25.0

A) use the results to plot a graph of length of spring against load.
b) use the graph to find the:
i) unloaded length of spring
ii) extensions produced by a 7.0n load
iii) load required to increase the length of the spring by 5.0cm

 

[Taylor_1989]

I have used the graph that i created for the first question and get 10.2cm but the ans is 10cm so where i see a 1.8 difference of the graph the book i use sees a 2cm, so i can work out the other questions without doing the first can someone tell me where I am going wrong?

 

[LawrenceC]

The plot should be linear. Your second point seems a little off. If you draw a line connecting points 1,3,4,5, it passes through 10 on the abyscissa.

Don't connect it back to 0,0 as you have done. It's length is not zero when the load is zero.

 

[Taylor_1989]

my maths is a little rusty could you please explain the abscissa, I can remember it has something to do with the x-axis for the carstine method ( I think ).

 

[LawrenceC]

The abyscissa is the horizontal axis. You should not be drawing a line from (0,0) to
(12,1). Your data point at (15.5,3) does not line up with the others so if you forget about it and extrapolate the others to the abyscissa, you'll get what you seek.