Rolling Bottle: Calculating Acceleration of Center of Mass

AI Thread Summary
The discussion focuses on calculating the acceleration of the center of mass for a hollow cylinder rolling on a surface as the paper is pulled with acceleration. The moment of inertia is initially miscalculated, with confusion between the center of mass and surface points. Key corrections include recognizing the correct moment of inertia formulas and ensuring torque calculations are consistent with the chosen axis. The method used for deriving angular acceleration is flawed due to this inconsistency. Overall, the conversation emphasizes the importance of clarity in applying physics principles to achieve accurate results.
Sonntag
Messages
1
Reaction score
0

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.
 

Attachments

  • Sketch.jpg
    Sketch.jpg
    5.8 KB · Views: 415
Physics news on Phys.org
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.
 
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top