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In Exercises 57–60, let R be the rectangular solid defined by

R = {(x, y, z) | 0 ≤ x ≤ 4, 0 ≤ y ≤ 3, 0 ≤ z ≤ 2}.

Assume that the density of R is uniform throughout, and find the moment of inertia about the x-axis and the radius of gyration about the x-axis.

Short Answer

Expert verified

The moment of inertia about the x-axis is Ix=104 and the radius of gyration about the x-axis isRx≈2.0816.

Step by step solution

01

Step 1. Given Information.

The given rectangular solid is defined byR={(x,y,z)∣0≤x≤4,0≤y≤3,0≤z≤2}.

02

Step 2. Find the moment of inertia about the x-axis. 

It is given that the density of R is uniform throughout, soÒÏ(x,y,z)=1.

Now, the moment of the inertia about the x-axis is,

Ix=∭Ω(y2+z2)ÒÏ(x,y,z)dvIx=∫04∫03∫02(y2+z2)dzdydxIx=∫04∫03∫02(y2+z2)dzdydxIx=∫04∫03y2∫02dz+∫02z2dzdydxIx=∫04∫032y2+83dydxIx=∫042∫03y2dy+83∫03dydxIx=∫0426dxIx=104

03

Step 3. Find the radius of the gyration.   

To find the radius of gyration about the x-axis, we have to find the mass of the rectangular solid:

M=∭RÒÏ(x,y,z)dxdydzM=∫04∫03∫02dxdydzM==(4−0)(3-0)(2-0)M=24

So, the radius of gyration is:

Rx=IxmRx=10424Rx≈2.0816

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