Where Should the Fulcrum Be Placed to Balance the Meter Stick?

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Homework Help Overview

The problem involves a meter stick with two weights placed at specific positions, and the goal is to determine the location of the fulcrum for balance. The subject area pertains to statics and torque in physics.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the concept of torque and its relation to the distances of the weights from the fulcrum. There are attempts to set up equations based on torque, but confusion arises regarding the differing radii for the two masses. Some participants suggest drawing diagrams to clarify the situation.

Discussion Status

The discussion is ongoing, with participants exploring various interpretations of the problem and attempting to clarify their understanding of torque and equilibrium conditions. Some guidance has been offered regarding the use of free body diagrams and the equations related to forces and moments.

Contextual Notes

There is mention of the challenge posed by the differing masses and the need for distinct torque calculations. Participants express uncertainty about the setup and the conditions necessary for equilibrium.

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Homework Statement


A metre stick of negligible mass has 1 .2kg mass at its 35cm mark and a .4kg mass at its 75cm mark. where will the fulcrum be if it is balanced?


Homework Equations


net torque = 0


The Attempt at a Solution


ive done more complicated questions then this but for some reason i can't figure this one out (logically its more complicated..). I don't know what to do since the radius of revolution will be different for both masses.
 
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Let be the fulcrum at mark "x" and write the torque of both weights with respect to the x mark.

ehild
 
i tried that but that keeps making the torque radius the same for both masses and it will never be in equilibrium
.2x+.4x=0 x=0 left gravity out because it just cancels
 
? I am sure I am missing something simple but i really can't think of it
 
What is torque at all? Is not it the product of force and the distance of the force line from the rotation axis?

ehild
 
yes that's what it is by definition but to be in equilibrium there has to be two different rotation radii since the masses are not equal. I cannot figure out what to do because of this?
 
make drawing.

ehild
 
i have it didnt help me
 
Show your drawing. Without it, I do not understand what is in your mind.

ehild
 
  • #10
the fulcrum goes at some unknown place between them. didnt bother labeling it because its such a simple drawing.
 

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  • #11
Show all the forces and their arms.

ehild
 
  • #12
you can draw it!


http://www.convertmpgtowmv.com" .
 
Last edited by a moderator:
  • #13
who can draw it-- wtf are you talking about??
 
  • #14
I gave up. I wanted a drawing something like this. I made it with Paint in 2 minutes.
d1=35 cm, d2= 75 cm, F1 = 1.2 g, F2=0.4 g, the pivot is at mark x.
What are the conditions of equilibrium?
How do you calculate the torque of a force F with respect to a point, say with respect to the left edge of the metre stick?


ehild
 
Last edited:
  • #15
this is a statics problem. What should you do with any statically determinate statics problem?

Answer:

Free Body Diagram

Sized for effect. Seriously, get used to drawing them now OP, they are so useful.
 
  • #16
net torque and force are 0, still i end up with two variable to solve for though
 
  • #17
pat666 said:
net torque and force are 0, still i end up with two variable to solve for though

You also have 2 equations.
 
  • #18
what are my two equations, i have T=rFsin(90) and T=Ia but i don't think i can use that
 
  • #19
Have you drawn a free body diagram?

There are two equations:

Sum of vertical forces.
Sum of moments.

You should have 2 unknowns, so those 2 equations are enough to solve the problem.
 

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