2.5 Exercises of Feyman lectures on Physics

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Homework Help Overview

The discussion revolves around a physics problem related to equilibrium involving a plank and a weight, as referenced from the Feynman lectures. Participants are examining the forces acting on the system, particularly in relation to a pulley setup and the associated free body diagrams.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Participants discuss the need for a free body diagram to analyze the forces acting on the plank. There are attempts to identify the forces involved, including weight and gravitational forces, and some participants express confusion about the correct representation of these forces.

Discussion Status

The discussion is ongoing, with some participants providing guidance on how to properly draw and label free body diagrams. There is a recognition of the need for clarity in understanding the forces at play, but no explicit consensus has been reached regarding the solution to the problem.

Contextual Notes

Some participants mention the challenge of understanding the material from the Feynman lectures, suggesting that additional resources may be beneficial. There is also a note that one participant is in middle school, which may influence their grasp of the concepts being discussed.

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Homework Statement
A uniform plank 1.5m long and weighting 3kg is pivotedat one end.The plank is held in equilibrium in a horizontal position by a weight and pulley arrangement.Find th e W needed to balance th plank.Neglect friction
Relevant Equations
no equation
I think that the W should be 3kg to be in equilibrium but in the book it said that id 3/√(2 I don't why
 
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The pulley rope is attached to the end of the plank I assume. So the first thing you do for any force problem is ___________ ?
 
the diagram
 
Yes the "free body" diagram.
 
ok well I know that the the pulley is aright triangle so the part that is conected to the plank forms a 45 angle and i think that's something important
 
Draw the free body diagram and show us the details .
Also first please see @berkeman comment and finish that up.
 
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I finish it
 
so thw W goes down and have an opposite reaction
 
  • #10
You need to draw a good complete free body diagram.
  1. It will include three forces acting on the plank, two of unknown magnitude.
  2. From the fact that the plank is stationary in two different ways two equations obtain.
  3. solve for the unknowns
If you desire further help you must show us your work.
 
  • #11
so the total forces are 5?
 
  • #12
please list the five. This is not a game of "twenty questions"
 
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  • #13
the Wx,Wy the gravity that affract the plank the opposite reaction of the gravity and the opposite reaction of Wx
 
  • #14
Please draw and submit "free body" diagram: Draw the plank with no external forces ("free body") and one by one add all the labelled vector forces acting ON the plank. Then show your result. Then we can discuss.
 
  • #15
paint physics.png
 
  • #16
physics.png
 
  • #17
physics1.png
 
  • #18
like this?
 
  • #19
Close. But on the first drawing make a labelled arrow representing each force and its position of application. Doesn't have to be pretty (you don't really need the pulley but you do need the angle).
 
  • #20
paint physics 2.png
 
  • #21
Draw a single arrow representing each and every force ON the plank (if the direction is wrong the vector will turn out negative) .
These are the tools of the trade. Has no one taught this to you previously (review as necessary!) ?
 
  • #22
sorry I am in middle school
 
  • #23
but the number of forces are correct
 
  • #24
sorry what do you mean only one arrow
 
  • #25
Ah, that's good to know. You are doing well then, but may need some basics . Do you have a text other than Feynman availible ? (don't get me wrong I adore RPF lectures but they are difficult to learn from at times)
 
  • #26
yes I have the volume 1 of feyman lectures on physics
 
  • #27
Can you get a copy of Tipler or Thornton or 0Sears,Zemansky or even Halliday,Resneck . Library??
 
  • #28
Those are books
 
  • #29
I think I got it
 
  • #30
thanks I will try to get a copy
 

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