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Homework Help: Springs in series and parallel : Problem for U

  1. Apr 21, 2007 #1
    I came across an objective question on the topic 'Springs in series and parallel' .. Have i asnwered it correctly?

    Q. A Force of 5Kg compresses 2 springs in series by 10 cm. What will be the compression when the same force acts on the same 2 springs but when the springs are in parallel?

    Choices >>
    1) 5 cm
    2) 10 cm
    3) 2.5 cm
    4) 20 cm

    MY ANSWER >> 2.5 cm

    Please correct me if I am wrong..
  2. jcsd
  3. Apr 21, 2007 #2
    You are correct !
    though it should have been mentioned that the springs are identical but as nothing is mentioned we can take them to be identical
  4. Apr 21, 2007 #3
    Thanks buddy...

    Oh yes, U r spot on.. I forgot to mention that the springs are identical..

    The logic I followed was >>

    In series,
    * The compression is 10 cm
    * This means each spring compresses by 5cm
    * Since the springs are in series, both the springs experience the full 5 kg
    * So, each spring compresses 1 cm for 1 kg (Spring constant=1)

    In parallel,
    * Now, the force is divided between the 2 springs
    * So, force acting on each spring is 2.5 N
    * So, in this case, the spring compresses to 2.5xSpring constant(1) = 2.5 cm

    Hope I am right with my logic too.. Sorry, I should have mentioned this earlier:biggrin:
  5. Apr 22, 2007 #4
    most welcome

    well....your logic seems correct but some problem in units.

    u say spring constant is 1??
    if its 1 it must be 1 cm/kg wt but in si it will be not be so

    but later you say the force on each spring is 2.5 N it can't be its 2.5kg wt

    otherwise your soln is correct

    n btw ...
    if you are preparing for some objective type examinatiom
    then you can use
    for series
    and parallel
    where k is equivalent spring constant
  6. Apr 23, 2007 #5
    Thanx chap..:approve:

    (Ooops, the 2nd force that I mentioned is 2.5 KG (Not Newton) ... by mistake I wrote it as 2.5N)
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