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    • Thread Starter

    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
    What is the extension for the pair of springs?

    is the answer 6 cm?

    oh wait no 2 springs so 6*2=12

    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

    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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