1. Not finding help here? Sign up for a free 30min 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!

A couple of statics questions

  1. Jul 2, 2004 #1
    Hi, I have a couple of questions from a statics assignment that I'm in need of help on. Here's what I have so far:

    http://216.170.11.226/pub/6131.jpg

    Two rods are connected by a slider block as shown. Neglecting the effect of friction, determine the couple Ma required to hold the system in equilibrium.

    And this is what I believe the forces are:

    http://216.170.11.226/pub/6131-2.jpg

    It would seem to me that the external forces are irrelevant to this problem, but I'm guessing not. What I came up with for this problem is:

    Sum of moments about B=0 => -25+Nd*271.89=0 => Nd=0.0919
    Sum of moments about A=0 => -.0919*150+Ma=0 => Ma=13.79 N*m

    I know the answer is Ma=15.22 N*m. I'm guessing that I also need to consider external forces or something.


    The next problem is

    http://216.170.11.226/pub/6129.jpg

    The double toggle mechanism shown is used in a punching machine. Knowing that the links AB and BC are each of length 150 mm, determine the couple M required to hold the system in equilibrium when Phi=20 (degrees).

    Once again, my analysis of the problem is:

    http://216.170.11.226/pub/6129-2.jpg

    Obvious things are:
    Dy+Ey+Ay+800=0
    Dx+Ex+Ax=0

    sum of moments about B of AB=0 => M+By*150*cos(30)+Bx*150*sin(30)=0

    Since AB is a two-force body, Bx=B*cos(30), By=B*sin(30) and A=-B.

    B'x=-Bx
    B'y=-By
    Cx=C*cos(30)
    Cy=C*sin(30)
    sum of moments about C of BC=0 => -B'x*150*sin(30)+By*150*cos(30)=0
    sum of moments about B of BC=0 => -Cy*150*cos(30)+Cx*150*sin(30)=0

    And so on and so forth. If I continue in this manner I figure I'll end up with something around 24 equations, there has got to be a simplier method. Any idea what that might be?

    Any hints or help would greatly be appreciated.

    Thanks
    -Aaron
     
  2. jcsd
  3. Jul 5, 2004 #2
    Ok, the first problem is easy, I just forgot to get a perpendicular distance to the force, so it works fine now.

    As for the second problem, I was thinking about just balancing the Fx, Fy, Ma, Md, and Me, but that doesn't seem to work either. Any suggestions would be appreciated.
     
  4. Jul 5, 2004 #3

    NateTG

    User Avatar
    Science Advisor
    Homework Helper

    Is [tex]N_D[/tex] supposed to be an applied force in that drawing?

    Can you list the terms you have for the net forces, and net torques, and which point they are about?
     
  5. Jul 7, 2004 #4
    Sorry, [tex]N_D[/tex] was an internal force from the collar. Thanks anyway, but I managed to figure this one out.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: A couple of statics questions
  1. A couple of questions (Replies: 4)

  2. A couple of questions (Replies: 9)

  3. A couple questions, (Replies: 6)

  4. Couple of Questions (Replies: 0)

Loading...