Equilibrium problem: Calculate the tension of each cord

  • #1
TheePhysicsStudent
21
17
Homework Statement
Was practising an equilibrium problem (and i have done quite a few like this one before and got them right) and I am unsure Where i have went wrong here
Relevant Equations
t1v + t2v = 2.8
1706958890868.png
The question
1706958924448.png
What I did
1706958951569.png
The answer
 
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  • #2
##\frac{\cos\theta}{\sin\theta}=?##
 
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  • #3
Not ##\tan## :smile:
(slow typist)
 
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  • #4
Also, $$\begin{align} & T_2\frac{\cos60^{\circ}\cos40^{\circ}}{\sin40^{\circ}}+
T_2\sin60^{\circ}=T_2\left(\frac{\cos60^{\circ}\cos40^{\circ}+\sin60^{\circ}\sin40^{\circ}}{\sin40^{\circ}}\right) \nonumber \\
& =T_2\frac{\cos(60^{\circ}-40^{\circ})}{\sin40^{\circ}} =T_2\frac{\cos20^{\circ}}{\sin40^{\circ}}.\nonumber
\end{align}$$
 
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  • #5
TheePhysicsStudent said:
A couple of things worth noting...

1. If you draw the force-triangle and use the sine rule, the problem takes only a few lines of simple working. (It’s a lot quicker and less error-prone than the method you used.)

2. You have forgotten the unit in your final answer - lose one mark!
 
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  • #6
Hanging toy.jpg
 
  • #7
To avoid any confusion, by 'force-triangle' (in Post #5) I meant this...
triangle.gif
 
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  • #8
Steve4Physics said:
To avoid any confusion, by 'force-triangle' (in Post #5) I meant this...
View attachment 339715
Wow thanks, I think this information may help speed time in lots of calculations i do
 
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  • #9
TheePhysicsStudent said:
Wow thanks, I think this information may help speed time in lots of calculations i do
Just in case it is not clear, when drawing a force polygon of forces in balance, the arrows join head to tail, as in @Steve4Physics' drawing.
You can also use them to find the resultant of a system of forces. In that case the resultant completes the polygon but its arrow is reversed.
 
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FAQ: Equilibrium problem: Calculate the tension of each cord

What is the first step in solving an equilibrium problem involving the tension of cords?

The first step is to draw a free-body diagram of the system. Identify all the forces acting on the object, including the tensions in the cords and any external forces like gravity. Label each force clearly and indicate their directions.

How do you apply the conditions for equilibrium in these problems?

For an object to be in equilibrium, the sum of all forces acting on it must be zero (translational equilibrium), and the sum of all torques about any point must also be zero (rotational equilibrium). Mathematically, this is represented as ΣF = 0 and Στ = 0.

How do you resolve the forces into their components?

To resolve the forces into their components, break each force into its horizontal (x-axis) and vertical (y-axis) components using trigonometric functions. For example, if a force F makes an angle θ with the horizontal, its components are Fcos(θ) in the x-direction and Fsin(θ) in the y-direction.

What equations do you set up to solve for the tensions in the cords?

Set up equations based on the sum of forces in both the horizontal and vertical directions being zero. For example, ΣFx = 0 and ΣFy = 0, where Fx and Fy are the components of the forces in the x and y directions, respectively. Solve these simultaneous equations to find the tensions in the cords.

How can you check if your solution is correct?

To verify your solution, ensure that the calculated tensions satisfy both the equilibrium conditions (ΣF = 0 and Στ = 0) and that they are consistent with the physical setup of the problem. Additionally, check that the units are correct and that the magnitudes of the tensions are reasonable given the context of the problem.

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