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Homework Help: Some questions.

  1. Nov 25, 2006 #1
    1. Three resistances of value 1,2 and 5 have to be connected in such a way that all are used once. Which value cannot be obtained?
    1) 17/3 2) 17/4 3) 17/6 4)17/7

    I know formulas for parallel and interconnected resistance. My teacher tells me that by looking at the options I can solve this. Pleasse help. I am not able to make out.

    2. In stretching a spring through 4 cm, 2 J work is done. If it compressed by 6 cm then amount of work will be?

    According to me its 3j but my book gives it 4.5 J. How come?

    3. A wooden cube (densit 0.60 g/cc) just dips inside the water if pressed with a force of 10 N. What must be the size of cube? (g= 10m/s^2)

    I have no idea.

    Please help :tongue2:
  2. jcsd
  3. Nov 25, 2006 #2


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    Homework Helper

    You should show some efforts in order to get help.

    Hint: regarding 2), what is the relation between work and the change of potential energy in a spring?
  4. Nov 25, 2006 #3
    I am sorry sir. I have problems. I am a student of class 9th. I take part in all the olympiads to learn new things. I have nothing to read except my own class text books. I just use the internet. Just imagine as to how can I think about something about which I dont have the slightest idea. I need help from you all (if its not a burden). Please try solving my questions and tell me about the topics and books or sites in which I could find relevant material.

  5. Nov 25, 2006 #4


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    Homework Helper

    First of all, you don't have to call me 'sir', not that I don't appreciate your politeness though. :smile:

    Second, for number 2), you should find this link useful: http://hyperphysics.phy-astr.gsu.edu/hbase/pespr.html" [Broken].
    Last edited by a moderator: May 2, 2017
  6. Nov 25, 2006 #5
    Thank you very very much for your help. You gave me exactly what I needed. Thanks a million times!
    Last edited by a moderator: May 2, 2017
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