Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Awesome pulley problem

  1. Aug 29, 2007 #1
    Awesome pulley problem!!!

    Hey, i just came across this pulley problem and thought it was easy to solve....on solving, my answers were not matching....!

    Check the attachment...

    There is a single string. Ignore the friction.
    The mass of the pulleys A, B & C is 1 Kg each.
    *ignore the dirty, bad diagram...what else can i do in windows!!!???*


    also post the method of doing...

    correct options are a,b & d...
     

    Attached Files:

    • phy.JPG
      phy.JPG
      File size:
      17.7 KB
      Views:
      117
  2. jcsd
  3. Aug 29, 2007 #2

    Danger

    User Avatar
    Gold Member

    No fair! Misleading title! I'm going to complain to the Mentors!
    I came here expecting something about a chicken cannon. :grumpy:

    Seriously, though, welcome to PF. Nothing can be done until your attachment is approved.
     
  4. Aug 29, 2007 #3

    HallsofIvy

    User Avatar
    Science Advisor

    Your diagram is excellent- just enlarge it. Note that we do require that you show what you have tried yourself and you must try. To get you started, I would recommend you lable the ropes between pulleys (and the forces for each), say x,y,z,u,v,w. I count 6such ropes and so 6 such forces.
     
  5. Aug 29, 2007 #4

    Danger

    User Avatar
    Gold Member

    Correction. Nothing can be done by non-Mentors, who can't see the attachments until they're approved. :tongue:
     
  6. Aug 29, 2007 #5
    hm...

    ok, but...
    hm...
    well, i cant work on my PC so well ...
    i mean i cant do high-end editing...Bad in computers....!
    i cant even scan the page of my notebook because i dont have a scanner!!!

    well, i will surely post what ive tried...veryy soon...!
    and, sorry....
    its pulleY...
    not pulleT
    !!!
     
  7. Aug 29, 2007 #6

    Danger

    User Avatar
    Gold Member

  8. Aug 29, 2007 #7
    Is C fixed?

    Have a think as to which are fixed, and (for the start) draw arrows on the diagram indicating which way the string will go.
     
  9. Aug 29, 2007 #8

    DaveC426913

    User Avatar
    Gold Member

    Yeah, you beat me to it.
     
  10. Aug 29, 2007 #9

    chroot

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    s/pullet/pulley/

    - Warren
     
  11. Aug 29, 2007 #10
    i really [tex]don't[/tex] want to sound stupid but please do attach some points to the cieling(if any) otherwise the system will fall don due to gravity(if any )


    anyways just use the fact that in a closed rigid system the tension(internal force) does no work.
    since tension on each pulley is known spped hence accelaration of each pulley is known
     
  12. Aug 29, 2007 #11
    There's an easy way for solving pulley problems, but I really don't know how to use that method.

    make an equation using all ropes distances(find relationships between them), and differentiate them.
    anyone knows that method?
     
  13. Aug 29, 2007 #12
    yes the constrain t method but that's just mathematical representation of what u think intutively
    for example consider the standard pulley problem of two masses say [tex]m_{1}[/tex] and [tex]m_{2}[/tex] hanging on two ends.
    now say one get's down by [tex]x[/tex] other by [tex]y[/tex] then since rope length is constsnt we have
    [tex]x+y=0[/tex]
    differentiating
    [tex]\frac{dx}{dt} + \frac{dy}{dt}=0[/tex]
    thus [tex]v_{m_{1}}=-v_{m_{2}}[/tex]
    differentiating again
    [tex]a_{m_{1}}=-a_{m_{2}}[/tex]
     
  14. Aug 29, 2007 #13
    I can't do that with more than two pulleys ><
     
  15. Aug 29, 2007 #14

    Danger

    User Avatar
    Gold Member

    You rat! Now my post just looks stupid. :frown:
    I'm glad that Dave was a witness to the original title. :tongue:
     
  16. Aug 30, 2007 #15
    what is that u couldn't solve
     
  17. Aug 30, 2007 #16
    hey, isn't there things like photoshop and paint? they are good programs that can help you to edit your pictures. try them! =)
     
  18. Aug 31, 2007 #17
    Um...correction...!

    sorry for the wrong image...well, not wrong...but incomplete...!
    The motion of pulleys or strings is not mentioned in the question...
     

    Attached Files:

    • phy.JPG
      phy.JPG
      File size:
      17.7 KB
      Views:
      82
    Last edited: Aug 31, 2007
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook