Need help finding angular momentum of a particle

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Homework Help Overview

The discussion revolves around calculating the angular momentum of a particle in a two-dimensional plane, given its position, velocity, and the force acting on it. The problem involves interpreting angles and vector components in the context of angular momentum.

Discussion Character

  • Conceptual clarification, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to clarify the interpretation of angles and the setup of the problem, particularly regarding the velocity vector and its angle. There are questions about the calculations and the origin of certain angles, such as the 195° mentioned in the original post.

Discussion Status

The discussion is ongoing, with participants seeking clarification on the problem's setup and expressing uncertainty about the interpretation of angles. Some guidance has been offered regarding the need for clearer descriptions and the use of LaTeX for symbols, but no consensus has been reached on the correct approach to the problem.

Contextual Notes

Participants note the absence of images and the potential ambiguity in the problem statement, which may affect the interpretation of angles and vectors. There is also a mention of homework rules regarding the presentation of the problem.

Ella1777
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1. At the instant of the figure, a 6.70 kg particle P has a position vector
session.quest2530192entrance1_N10034.mml
of magnitude 4.30 m and angle θ1 = 43.0° and a velocity vector
session.quest2530192entrance1_N10056.mml
of magnitude 3.40 m/s and angle θ2 = 32.0°. Force
session.quest2530192entrance1_N10078.mml
, of magnitude 7.40 N and angle θ3 = 32.0° acts on P. All three vectors lie in the xy plane. About the origin, what are the magnitude of (a) the angular momentum of the particle
2. L=r x p=r x m x v3. φ3 = Θ1 + Θ3 = 43.0º + 32.0º = 75.0º
φ2 = 270º - Θ1 - Θ2 = 270º - 43º - 32º = 195º
φ1 = Θ1 = 43.0º


r = 4.30m*(cos43.0º i + sin43.0º j)
F = 7.40N*(cos75.0º i + sin75.0º j)
v = 3.40m/s*(cos195º i + sin195º j) L = r x p = r x m*v
where L, r, p and v are vectors.
L = 4.30m * 6.70kg * 3.40m/s * (cos43.0º i + sin43º j) x (cos195º i + sin195º j)
L = 4.30m * 6.70kg * 3.40m/s * (cos43.0*sin195 - sin43.0*cos195)k
L = L = 4.30m * 6.70kg * 3.40m/s * 0.469471562 k = 45.98661738 k kg·m²/s
which has magnitude 46.0 kg·m²/s
Although this seems to be wrong what am i doing wrong?
 
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The statement of the problem is hard to interpret. There are no images. Also, please use LaTeX for symbols.
 
Ella1777 said:
magnitude 3.40 m/s and angle θ2 = 32.0°

Ella1777 said:
φ2 = 270º - Θ1 - Θ2 = 270º - 43º - 32
Since the images don't work, looks like you need to describe what this 32.0° angle is.
I would have guessed it meant the angle anticlockwise from the positive x axis, but that is not how you have treated it.
 
Where does the 195° come from? It looks like v = 3.40 m/s (cos 32° i + sin 32° j).
 
Dr Dr news said:
Where does the 195° come from? It looks like v = 3.40 m/s (cos 32° i + sin 32° j).
Ella treated the 32 degrees as though it is additional to the 43 degrees, but without the diagram (or clear description) we cannot tell if that is appropriate.
 

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