One Knot Problem - Find two unknown masses

  • Thread starter Wolfin
  • Start date
In summary, the conversation involves finding the masses of M1 and M2 given the mass and acceleration of M3, as well as the vertical angles between M3 and M1 and M2. The equations F = ma and F = ma sin(Θ) are mentioned, and the person has attempted to solve the problem using algebra. A hint is given to consider the vector components of force, which leads to the solution: solve for m1 and m2 in the x and y components, make them equal to each other, and then substitute to solve for m1.
  • #1
Wolfin
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Homework Statement



See the attachment.
We're asked to find the masses of M1 and M2. I'm wondering how this is possible, 'cause there's two variables and only one known? Do I have to use sine/cosine law?

m3 = 0.1998 kg
T3 = (0.1998 kg)(-9.80 m/s^2) = -1.96 N

Vertical angle A (between T3 and T1) = 38.0 degrees
Vertical angle B (between T3 and T2) = 27.0 degrees

Homework Equations



F = ma
F = ma sin (Θ)

The Attempt at a Solution



I tried to solve with algebra:

m1 g sin (A) + m2 g sin (B) = m3 g

Gravity cancels.

m1 sin (A) + m2 sin (B) = m3 g

...And that's about as far as I got :(

Any help/hints would be appreciated muchly.. the Physics head decided we should only get two days to do our labs.. it's due tomorrow.
 

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  • #2
Hint: Force is a vector...it will have both horizontal and vertical components, and both must be zero for the mass m3 not to move...
 
  • #3
Yeah, I got it now. Had to:

Solve for m1 in the equation for the sum of all the x components and the equation for the sum of all the y components.

Then make them equal to each other, solve definitively for m2, then substitute to solve for m1.

Thanks for the help!
 

1. What is the One Knot Problem?

The One Knot Problem is a mathematical problem that involves finding two unknown masses connected by a string or rope, where the string is tied in a single knot. The goal is to find the masses of the objects based on the tension in the string and the angle of the knot.

2. How is the One Knot Problem solved?

The One Knot Problem can be solved using equations from Newton's laws of motion and trigonometry. By setting up equations for the forces acting on the knot, we can solve for the unknown masses.

3. What information is needed to solve the One Knot Problem?

To solve the One Knot Problem, we need to know the tension in the string and the angle of the knot. These values can be measured or given in the problem.

4. Are there any assumptions made when solving the One Knot Problem?

Yes, there are a few assumptions made when solving the One Knot Problem. These include assuming the string is massless, neglecting any friction between the string and the objects, and assuming the knot is tied perfectly at the center of mass of the objects.

5. What are some real-world applications of the One Knot Problem?

The One Knot Problem can be applied in various fields such as engineering, physics, and architecture. It can be used to determine the masses of objects in tension systems, such as suspension bridges or cranes. It can also be used to analyze the forces acting on objects connected by ropes or cables, like in rock climbing or sailing.

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