1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Min force to lever to lift weight

  1. Aug 31, 2015 #1
    1. The problem statement, all variables and given/known data
    upload_2015-8-31_22-49-3.png

    2. Relevant equations
    Concept of couple?

    3. The attempt at a solution
    First, I calculated the couple about disc, though I'm not sure if I can use this approach. Since 900 N is pulling the string of pulley downwards, I take the couple about disc as 900 x 0.4, which gives me 360 Nm. To balance this couple, the couple by F must be equal to 360. So 1.2 x F = 360 which gives me 300 N as the answer. But I'm wrong, since the answer is B. Where did I go wrong?
     
  2. jcsd
  3. Aug 31, 2015 #2

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Any particular reason for using diameter?
     
  4. Aug 31, 2015 #3
    I thought the 900 N exerts a couple on the disc, though I'm not sure. I'm just guessing.
     
  5. Aug 31, 2015 #4

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    What are/would be the two elements of the couple?
     
  6. Aug 31, 2015 #5
    Two forces acting in opposite directions separated by a perpendicular distance.
     
  7. Aug 31, 2015 #6

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    What specific forces? And what distance?
     
  8. Aug 31, 2015 #7
    In this case there's only one force which is 900 N rotating the disc in anticlockwise direction.
     
  9. Aug 31, 2015 #8

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    What's holding the disc?
     
  10. Aug 31, 2015 #9
    The lever turning in opposite direction?
     
  11. Aug 31, 2015 #10

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    What's the "spindle" doing?
     
  12. Aug 31, 2015 #11
    Transferring the energy?
     
  13. Aug 31, 2015 #12

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    No sideways forces on it?
     
  14. Aug 31, 2015 #13
    I totally don't know. From the picture, as the spindle rotates, it turns discs in opposite direction to the wight of 900 N on disc.
     
  15. Aug 31, 2015 #14

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    What happens when you pull the starter rope on a lawnmower without putting your foot on the mower to hold it in place?
     
  16. Aug 31, 2015 #15
    The lawnmower will jump?
     
  17. Aug 31, 2015 #16

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Any particular direction?
     
  18. Aug 31, 2015 #17
    I've never used a lawnmower before:-p so I'm not too sure.It will jump away from the person pulling it?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Min force to lever to lift weight
  1. Lift force (Replies: 1)

Loading...