Confusing Angular Momentum problem with Door

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SUMMARY

The discussion centers on calculating the final angular speed of a solid wood door after being struck by a mass of sticky mud. The door, measuring 1.00 m in width and 2.00 m in height, has a mass of 49.0 kg, while the mud has a mass of 0.500 kg and strikes the door at 14.0 m/s. Key principles include the conservation of angular momentum, as the hinge prevents linear momentum conservation, and the inelastic nature of the collision, which does not conserve energy. Participants emphasize the need to correctly calculate the angular momentum of the mud and the moment of inertia of the system.

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  • Understanding of angular momentum and its conservation principles.
  • Familiarity with moment of inertia calculations for rigid bodies.
  • Knowledge of inelastic collisions and their effects on energy conservation.
  • Basic physics concepts related to rotational motion.
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  • Study the calculation of angular momentum for point masses and rigid bodies.
  • Learn about the moment of inertia formulas for various shapes, including doors and point masses.
  • Review inelastic collision dynamics and their implications on momentum and energy.
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chaostheory13
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Homework Statement



A solid wood door of width 1.00 m and height 2.00 m is hinged along one side and has a total mass of 49.0 kg. Initially open and at rest, the door is struck at its center by a handful of sticky mud with mass 0.500 kg, traveling perpendicular to the door at 14.0 m/s just before impact. Find the final angular speed of the door with the mud stuck to it.

I'm totally lost on this one. Four different approaches, four very different answers, all of them wrong.

Please help.
 
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As the door is hinged, there is a force acting from the hinge so the momentum will not conserve during the impact. Neither the energy will conserve as there is an "inelastic" collision between mud and door. There is one quantity that conserves: the total angular momentum of the system door+ mud ball. Calculating the angular momentum both the piece of mud and the door with respect to the hinge, their sum is the same before and after the impact.

ehild
 
I believe I tried that, but I must be doing something wrong with that angular momentum calculation.

How do you calculate the angular momentum of the mud before it hits the door? Is it (mass of mud * velocity of mud * distance from the hinge)? Since it hits at the middle, that distance would then be 0.5 meters. And then when calculating the moment of inertia of the system that's (1/3)MR^2 for the door and (MR^2) for the mud as a point mass.

Yet something must be incorrect because using these equations isn't generating the correct answer.
 

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