Moment of Inertia? Potential and Kinetic Energy? Anybody awake?

Click For Summary

Homework Help Overview

The discussion revolves around the concepts of moment of inertia and the velocities of different objects rolling down an incline. The objects in question include a hoop, a solid cylinder, and a sphere, with a focus on how their moments of inertia affect their motion.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to derive equations for the velocities of a hoop and a solid cylinder as they roll down an incline. They are also discussing the implications of different moments of inertia on the velocities of these objects compared to a sphere.

Discussion Status

Some participants have raised questions about the correctness of the moment of inertia for the hoop and are exploring the reasons why the velocities of the rolling objects should differ. There is an ongoing examination of the statements regarding the effects of mass distribution on moment of inertia and rotational kinetic energy.

Contextual Notes

There appears to be some confusion regarding the moment of inertia values provided for the hoop, with differing opinions on whether it should include a factor of 1/2. Additionally, participants are considering the implications of the mass and radius being the same for all objects in the context of their velocities.

riseofphoenix
Messages
294
Reaction score
2
I don't know how to answer these - please please please help!

Consider the following objects of mass m rolling down an incline of height h.

(a) A hoop has a moment of inertia I = (1/2)mr2. What is the equation for the velocity vhoop of the hoop at the bottom of the incline? (Use the following as necessary: m, h, r, and g.)

vhoop =

(b) A solid cylinder has a moment of inertia I = (1/2)mr2. What is the equation for the velocity vcylinder of the cylinder at the bottom of the incline? (Use the following as necessary: m, h, r, and g.)

vcylinder =

(c) We know that the velocity of the sphere at the bottom of the ramp is √ [ (10gh)/7 ] from which we can conclude that the mass of the sphere does not affect the velocity of the sphere. Which of the following statements help to explain why the equations for the velocity in the case of the rolling cylinder and rolling hoop should be different from each other and from that of the sphere? (Select all that apply.)

a) Even if all three objects had the same mass and the same radius, they would all have different moments of inertia and therefore different rotational kinetic energies, which will affect the velocity of the object as it rolls down the incline.
b) The rotational kinetic energy of a solid depends on its moment of inertia I, which will affect the velocity of the object as it rolls down the incline.
c) The moment of inertial of a sphere, cylinder and hoop are different because of how the mass is distributed in each of these objects. This would affect the velocity of the object as it rolls down the incline.
 
Physics news on Phys.org
riseofphoenix said:
I don't know how to answer these - please please please help!

Consider the following objects of mass m rolling down an incline of height h.

(a) A hoop has a moment of inertia I = (1/2)mr2. What is the equation for the velocity vhoop of the hoop at the bottom of the incline? (Use the following as necessary: m, h, r, and g.)

vhoop =

(b) A solid cylinder has a moment of inertia I = (1/2)mr2. What is the equation for the velocity vcylinder of the cylinder at the bottom of the incline? (Use the following as necessary: m, h, r, and g.)

vcylinder =

(c) We know that the velocity of the sphere at the bottom of the ramp is √ [ (10gh)/7 ] from which we can conclude that the mass of the sphere does not affect the velocity of the sphere. Which of the following statements help to explain why the equations for the velocity in the case of the rolling cylinder and rolling hoop should be different from each other and from that of the sphere? (Select all that apply.)

a) Even if all three objects had the same mass and the same radius, they would all have different moments of inertia and therefore different rotational kinetic energies, which will affect the velocity of the object as it rolls down the incline.
b) The rotational kinetic energy of a solid depends on its moment of inertia I, which will affect the velocity of the object as it rolls down the incline.
c) The moment of inertial of a sphere, cylinder and hoop are different because of how the mass is distributed in each of these objects. This would affect the velocity of the object as it rolls down the incline.
The moment of inertia for the hoop is mr2, not 1/2 there.
 
Last edited:
SammyS said:
The moment of inertia for the hoop is mr2, no 1/2 there.

Oh oops, you're right..
Do you happen to know the answer to part a, b, and c though?
 
SammyS said:
The moment of inertia for the hoop is mr2, no 1/2 there.

also, isn't part c all three of them (choices a, b, and c)?
 

Similar threads

  • · Replies 21 ·
Replies
21
Views
5K
  • · Replies 40 ·
2
Replies
40
Views
6K
Replies
8
Views
15K
  • · Replies 5 ·
Replies
5
Views
1K
  • · Replies 16 ·
Replies
16
Views
2K
Replies
4
Views
1K
Replies
11
Views
4K
  • · Replies 4 ·
Replies
4
Views
8K
Replies
2
Views
2K
Replies
39
Views
4K