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2012 F=ma problem 21

by ksrivatsan
Tags: 2012
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ksrivatsan
#1
Jan21-13, 01:22 PM
P: 2
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?

1. The problem statement, all variables and given/known data
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

2. Relevant equations

F=kx

3. 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...?
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Doc Al
#2
Jan21-13, 01:49 PM
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Quote Quote by ksrivatsan View Post
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.
ksrivatsan
#3
Jan21-13, 09:05 PM
P: 2
Thanks Doc Al!


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