Rolling Bottle: Calculating Acceleration of Center of Mass

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SUMMARY

The discussion focuses on calculating the acceleration of the center of mass for a hollow cylinder (an empty bottle) rolling on a surface when a paper is pulled with acceleration 'a'. Key equations include the moment of inertia in the center of mass, defined as I_C = 1/2 M R^2, and the moment of inertia on the surface, I_S = 3/2 M R^2. The correct expression for angular acceleration is α = F/(3/2 M R), leading to the acceleration of the center of mass as a_s = (2/3)(F/M). The discussion highlights the importance of using consistent axes when calculating torque and angular acceleration.

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  • Understanding of rotational dynamics and torque
  • Familiarity with moment of inertia concepts for hollow cylinders
  • Knowledge of angular acceleration calculations
  • Ability to analyze non-inertial reference frames
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  • Learn about torque and its relation to angular acceleration in different axes
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Sonntag
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Homework Statement


There is an empty bottle described as an hollow cylinder, that lies on a paper. Now the paper is pulled with an acceleration a, so that the bottle starts rolling perfectly on the paper. (Have a look at the figure.)

Homework Equations


Calculate the acceleration of the center of mass.

The Attempt at a Solution


Moment of inertia in the center of mass: ##{I_C = 1/2 M R^2}##
Moment of inertia in the center of mass on the surface: ##{I_S = 3/2 M R^2}##
Torque: ##{|\bf{M}| = |\bf{R}| |\bf{F}|}##
Angular acceleration: ##{\alpha = \dfrac{M}{I_S} = \dfrac{F}{3/2 M R}}##
acceleration of the center of mass: ##{a_s = \alpha R = 2/3 \dfrac{F}{M}} ##I have the feeling that my answer isn't the intended of the question. Mistakes? More to do? I hope on your answers and thoughts.
 

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Hint: Look at things from the (non-inertial) frame of the paper. (Note also that it's a hollow cylinder, so correct your formula for moment of inertia.)
 
Sonntag said:
Moment of inertia in the center of mass: ##{I_C = 1/2 M R^2}##
Moment of inertia in the center of mass on the surface: ##{I_S = 3/2 M R^2}##
I don't understand the expression "Moment of inertia in the center of mass on the surface"
i assume you mean
Moment of inertia about the center of mass: ##{I_C = 1/2 M R^2}##
Moment of inertia about a point on the surface: ##{I_S = 3/2 M R^2}##​
That would be true, as Doc Al points out, for a solid cylinder. But leaving that aside, your method still gave the wrong answer. The reason is that your expression for torque gives the torque about the mass centre. You cannot divide the torque about one axis by the MoI about a different axis to get the angular acceleration.
You can use Doc Al's method, or just be consistent about axes.
 

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