How Do You Calculate the Moment of Inertia for a Cone?

In summary, the conversation is about finding the moment of inertia of a right circular cone of radius r and height h and mass m. The equation for moment of inertia is I = ∫r2 dm. The attempt at a solution involves finding the density (p) and setting up a double integral problem with the cone's longitudinal axis as the x-axis, using a ring for the dV. However, the person forgot to include the factor of r2 in front of dm in the integral, resulting in only finding the mass of the cone. The hint suggests setting up the problem with a ring for dV and asking for more hints if needed.
  • #1
jforce93
26
0

Homework Statement


Find the moment of inertia of a right circular cone of radius r and height h and mass m


Homework Equations



I = ∫r2 dm
V = 1/3*π*r2*h

The Attempt at a Solution


Assume density is p

dm = p dv
divide both sides by dr
dm/dr = p dv/dr

dm/dr = p (d/dr * 1/3*π * r2*h)
so
dm/dr = p(2/3)*πrh
so:
dm = (2/3)pπrh dr

Sub that into the moment of inertia equation

∫(2/3)pπrh dr = I

I = (1/3) pπr2h
p = m/v
I = (1/3)(m/v)πr2h
I = v*(m/v)
I = m

What am I doing wrong?
 
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  • #2
Hint: Set the problem up as a double integral problem. Lay the problem out with the cone's longitudinal axis being the x-axis. Use a ring for your dV.

If you need more hints, let me know.
 
  • #3
You forgot the factor of r2 multiplying dm. What you found was [itex]\int dm[/itex], which unsurprisingly turns out to equal the mass of the cone.

About what axis are you supposed to be calculating the moment of inertia?
 

Related to How Do You Calculate the Moment of Inertia for a Cone?

1. What is the moment of inertia for a cone?

The moment of inertia for a cone is a measure of its resistance to rotation around a specific axis. It is a property that depends on the mass distribution and geometry of the cone.

2. How is the moment of inertia for a cone calculated?

The moment of inertia for a cone can be calculated using the formula I = (3/10)mr^2, where m is the mass of the cone and r is the radius of the circular base of the cone.

3. Does the height of the cone affect its moment of inertia?

Yes, the height of the cone does affect its moment of inertia. As the height increases, the moment of inertia also increases. This is because the weight of the cone is distributed further away from the axis of rotation, resulting in a larger moment of inertia.

4. How does the moment of inertia for a cone compare to that of a cylinder?

The moment of inertia for a cone is smaller than that of a cylinder with the same mass and height. This is because a cone has a smaller radius at the top, resulting in a smaller distribution of mass away from the axis of rotation.

5. What is the significance of the moment of inertia for a cone?

The moment of inertia for a cone is an important concept in physics and engineering. It is used to calculate the rotational motion and stability of objects, such as cones, in various applications. It also plays a role in determining the amount of force needed to rotate a cone or to keep it in a steady rotation.

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