Mass Moment of inertia of a cylinder with 4 holes?

[qpham26]

Homework Statement

Hi I was reviewing for my final and I came across this problem:

Problem:
Basically there is a 6in long cylinder with dia = 24in
Given weight density: 490 lb/ft^3

Each Hole is drilled symmetrically, each has 6in dia and equally space around a 10in dia circle concentric with the cylinder.

This is the picture of the frontview of the cylinder: https://lh4.googleusercontent.com/-8m1r4npC7cg/T11OqGF6qhI/AAAAAAAAABY/4v2HCrEqhd4/s333/cyinder.png Thanks for your time and consideration.
Appreciate it!

Homework Equations

The Attempt at a Solution

Approach
So what I would do is:
-First get that weight density into mass density by dividing it by 32.2
-Then find the mass of the cylinder without holes.
-Find mass of each holes.
-calculate the M of I of each hole about the center axis (parallel axis theorem)
-calculate the M of I of the whole solid cylinder (no holes)
-subtract the M of I of the holes from the whole cylinder

Will I get the correct answer based on the technique above?

 

[ehild]

That is a correct approach.

ehild

 

[qpham26]

Thanks and for the mass of the cylinder, the unit is slug right?

Thanks again.

 

[ehild]

I am sorry, I am not familiar with imperial units. But Wikipedia says it is slug.

The slug is a unit of mass associated with Imperial units. It is a mass that accelerates by 1 ft/s2 when a force of one pound-force (lbF) is exerted on it.

http://en.wikipedia.org/wiki/Slug_(mass )

ehild

 

[anjuv]

Homework Statement

Hi I was reviewing for my final and I came across this problem:

Problem:
Basically there is a 6in long cylinder with dia = 24in
Given weight density: 490 lb/ft^3

Each Hole is drilled symmetrically, each has 6in dia and equally space around a 10in dia circle concentric with the cylinder.

This is the picture of the frontview of the cylinder: https://lh4.googleusercontent.com/-8m1r4npC7cg/T11OqGF6qhI/AAAAAAAAABY/4v2HCrEqhd4/s333/cyinder.png


Thanks for your time and consideration.
Appreciate it!

Homework Equations

The Attempt at a Solution

Approach
So what I would do is:
-First get that weight density into mass density by dividing it by 32.2
-Then find the mass of the cylinder without holes.
-Find mass of each holes.
-calculate the M of I of each hole about the center axis (parallel axis theorem)
-calculate the M of I of the whole solid cylinder (no holes)
-subtract the M of I of the holes from the whole cylinder

Will I get the correct answer based on the technique above?

yah...
this only is the right way of solving it.