Help Solve 2012 F=ma Problem 21

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The discussion revolves around solving problem 21 from the 2012 F=ma exam, which involves a spring system with a platform and multiple springs. The user seeks assistance in determining how much the height of the spring system changes when a ball is added. The solution involves calculating the compression of the bottom springs, which act as a single spring with a combined spring constant, and the compression of the top spring. The total compression is found by adding the individual compressions of the springs. The correct answer to the problem is 0.100 m.
ksrivatsan
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Hi,

I'm just training for the 2013 F=ma exam, and I took some old exams. I tried to do the 2012 exam, and could not figure out problem 21. Can anyone help me, please?

Homework Statement


A spring system is set up as follows: a platform with weight 10 N is on top of two springs, each with a spring constant of 75 N/m. On top of the platform is a third spring with spring constant 75N/m. If a ball with weight of 5.0 N is fastened to the top of the third spring and then slowly lowered, by how much does the height of the spring system change?

(A) 0.033 m
(B) 0.067 m
(C) 0.100 m (correct answer)
(D) 0.133 m
(E) 0.600 m

Homework Equations



F=kx

The Attempt at a Solution


The bottom springs act as one spring with K=150 N/m, thus will contract 0.033 m under the weight
The top spring will compress 0.067 m under the weight
so is it just addition...?
 
Last edited:
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ksrivatsan said:
The bottom springs act as one spring with K=150 N/m, thus will contract 0.033 m under the weight
The top spring will compress 0.067 m under the weight
so is it just addition...?
Yes, that's all there is to it. You are just combining the two compressions to get the total compression.
 
Thanks Doc Al!
 
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