How Is the Total Angular Momentum of a Rotating Dumbbell Calculated?

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SUMMARY

The total angular momentum of a rotating dumbbell can be calculated using the formula L = wI, where L is angular momentum, w is angular speed, and I is the moment of inertia. For a dumbbell consisting of two balls with masses of 1.0 kg and 3.0 kg, rotating about a fixed vertical axis, the moment of inertia I is determined by I = mr², with r being the distance from the axis of rotation. Given an angular speed of 1/π revolutions per second, the total angular momentum is calculated to be 2 kg·m²/s.

PREREQUISITES
  • Understanding of angular momentum and its significance in rotational dynamics.
  • Familiarity with the moment of inertia calculation for point masses.
  • Knowledge of angular speed and its units of measurement.
  • Basic algebra for manipulating equations involving physical quantities.
NEXT STEPS
  • Study the derivation of the moment of inertia for various shapes and configurations.
  • Learn about the conservation of angular momentum in closed systems.
  • Explore the effects of changing mass distribution on angular momentum.
  • Investigate real-world applications of angular momentum in engineering and physics.
USEFUL FOR

Students in physics, particularly those studying rotational dynamics, as well as educators and anyone interested in the principles of angular momentum in mechanical systems.

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Homework Statement


A dumbbell consists of two small balls attached to the ends of a 1.0m rod of negligible mass. Ball1 has a mass of 1.0kg and ball2 has a mass of 3.0kg. The dumbbell rotates about a fixed vertical axis midway between the balls, with an angular speed of 1/pi rev/s. What is the total angular momentum of the dumbbell?


Homework Equations




The Attempt at a Solution



I=mr^2
L=wI
w=2 (since the angular speed is 1/pi rev/s?)
r^2=0.25m
m=4kg
L=2 kg*m²/s
would that be right?
 
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Seems OK to me.
 
Perfect.
 

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