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# Question on materials for A-level physics. Watch

1. I didn't know how to answer this question could someone please break it down for me on how to do it?

A spring extends by 9 cm when a force of 6 N is applied. The limit of proportionality is
not exceeded.
Another identical spring is joined end to end with this spring and a force of 4 N is
applied.
What is the extension for the pair of springs?
2. is the answer 6 cm?
3. oh wait no 2 springs so 6*2=12
4. the way i worked it out it:
extension = 9
force = 6
F=k delta L
6= 9k
k= 2/3

when springs are in series the force is equal throughout
so on each spring will be a force of 4N
so for one spring:
f= k delta L
4 = 2/3 delta L
delta L = 6
so for 2 springs 6*2=12cm
5. The spring constant is the same. so the spring constant is 2/3. So the new spring is connected in series so therefore the total extension should be 9+x. Using f=kx, we can substitute 4=2/3 x (9+x). when you solve this you get x=3. therefore the total extension of the pair of strings in series is 9+3=12cm

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