Determining angular momentum of a point mass.

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SUMMARY

The discussion focuses on calculating the angular momentum of a point mass in the xy plane, specifically a 2.00 kg body with a velocity of v=(7.00i-2.00j) m/s and a position vector r=(2.00i-1.00j) m. The correct formula for angular momentum is L = r x p, where p = mv. The final angular momentum is determined to be 6.00k kgm²/s, emphasizing the importance of using the vector cross product rather than scalar multiplication.

PREREQUISITES
  • Understanding of vector operations, specifically the cross product.
  • Familiarity with the concepts of linear momentum and angular momentum.
  • Knowledge of unit vector notation in physics.
  • Basic principles of mechanics involving point masses.
NEXT STEPS
  • Study the properties and applications of the vector cross product.
  • Learn about angular momentum in three dimensions, including L = r x p in more complex scenarios.
  • Explore the relationship between linear momentum and angular momentum in physics.
  • Review examples of angular momentum calculations for various systems, including rigid bodies.
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Students studying physics, particularly those focusing on mechanics, as well as educators and tutors looking to clarify concepts related to angular momentum and vector operations.

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Homework Statement



The velocity of a 2.00 kg body moving in the xy plane is given by v=(7.00i-2.00j) m/s. Its position vector is r=(2.00I-1.00j) m. Calculate its angular momentum (magnitude and direction) about the origin (kgm2/s). Express your answer in unit vector notation.


Homework Equations



L=rp
p=mv
..
L=Iω?


The Attempt at a Solution



I attempted to use L=rp=rmv and then substituted in my conditions. I got (28.0i + 4.00j) kgm2/s but the answer is apparently 6.00k. Where am I going wrong?
 
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You are dealing with vectors, not scalars.
Therefore the product rv should really be r x v. (x being the vector cross product).

A 2 dimensional cross product can be written as
r x v = r1 v2 - r2 v1 , where 1 and 2 simply denote the components of the vector: 1 for the i component, 2 for the j.

R.
 

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