Mechanics- connected particles

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Discussion Overview

The discussion revolves around a mechanics problem involving connected particles, specifically focusing on a horizontal bar supported by vertical rods and a mass hanging from it. Participants are attempting to determine the tension in the rods based on the forces acting on the system.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant calculates the tension in the middle rod (T3) as 40N and seeks assistance in finding the tensions in the other two rods (T1 and T2).
  • Another participant suggests sketching a free body diagram (FBD) to analyze the forces acting on the bar, indicating that the sum of the tensions (T1 + T2) must equal the weight of the bar and the hanging mass.
  • It is noted that T1 + T2 equals 50N, with T3 confirmed as 40N.
  • One participant proposes that T1 and T2 are equal to 25N each, reasoning that T3 is located at the midpoint of the bar.
  • Another participant questions the reasoning behind the equal tensions, prompting a discussion about translational and rotational equilibrium.
  • A later reply suggests looking up concepts related to translational and rotational equilibrium for further understanding.

Areas of Agreement / Disagreement

Participants generally agree on the calculations of the tensions but differ in their explanations of why T1 and T2 are equal, with some seeking a deeper understanding of the underlying physics principles.

Contextual Notes

There are unresolved assumptions regarding the application of equilibrium principles and the specific conditions under which the tensions are derived.

Shah 72
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A horizontal bar of mass 1kg hangs from a pair of parallel vertical rods of negligible mass, attached to either end of the bar. A third vertical rod is connected to the middle of the bar and a 4kg mass hangs from this below the rod. Work out the tension in each of the rods.
I got the tension in the third vertical rod= 40N. I don't know how to find the tension of the other two rods.
 
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did you sketch a FBD?

forces acting on the 1 kg bar …

$T_1+T_2$ up, $1g + T_3$ down
 
skeeter said:
did you sketch a FBD?

forces acting on the 1 kg bar …

$T_1+T_2$ up, $1g + T_3$ down
T1+T2=50N, T3=40N
 
Shah 72 said:
T1+T2=50N, T3=40N

so …

$T_1 =$ ?

$T_2 =$ ?

… and why?
 
skeeter said:
so …

$T_1 =$ ?

$T_2 =$ ?

… and why?
T1=T2 = 25 as T3 is at the midpoint of the horizontal bar
 
yes, but that’s not the “physics” reason … what do you know about translational and rotational equilibrium?

recommend you look them up if you haven’t heard those terms before
 
skeeter said:
yes, but that’s not the “physics” reason … what do you know about translational and rotational equilibrium?

recommend you look them up if you haven’t heard those terms before
Sure. Thanks!
 

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