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Let Tbe rectangular region with vertices (0,0),(1,1),and(1,-1)

If the density at each point in Tis proportional to the point’s distance from the x-axis, find the moments of inertia about the x- and y-axes. Use these answers to find the radii of gyration of Tabout the x- and y-axes.

Short Answer

Expert verified

Moment of Inertia is Iy=k5and Ix=k10

Mass of region is m=k3

Radius of gyration isRx=310,Ry=35

Step by step solution

01

Given Information

Vertices of triangular region are (0,0),(1,1),and(1,-1)

Densityrole="math" localid="1653994140071" ÒÏ(x,y)=ky

02

MOI about y axis

Iy=∬Ωx2ÒÏ(x,y)dA

Putting limits Iy=∫01∫-xxx2kydydx[ÒÏ(x,y)=ky]

As per figure

Iy=2∫01∫0xx2kydydx

Iy=2k∫01y220xx2dy

Iy=k∫01x4dy

Iy=kx5501

Iy=k5

03

MOI about x axis

It is expressed as:

Ix=∬Ωy2ÒÏ(x,y)dA

Ix=∫01∫-xxy2kydydx[ÒÏ(x,y)=ky]

As region is symmetric about xaxis

Ix=2∫01∫0xy2kydydx

Ix=2k∫01∫0xy3dydx

Ix=k2∫01x4dx

Ix=k2x5501

Ix=k10

04

Mass of triangular region

It is given by m=2∫01∫0xkydydxm=∬ΩÒÏ(x,y)dA

m=2k∫01y220xdx

m=k∫01x2dx

m=kx3301

m=k3

05

Radius of gyration

It is given by

Rx=IxmandRy=Iym

Rx=k/10k/3andRy=k/5k/3

Rx=310,Ry=35

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