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Determine the mass moment of inertia of the thin plate about the axis perpendicular to the...

Determine the mass moment of inertia of the thin p

Determine the mass moment of inertia of the thin plate about the axis perpendicular to the page and passing through point O assuming the material has a mass per unit area of 20 kg/m2.
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Concepts and reason

Mass moment of inertia:

It is calculated by multiplying the point mass with the square of the distance from the axis of rotation.

Parallel axis theorem:

It states that the moment of inertia about a point is equal to sum of the moment of inertia about the centroid of the section and the product of area of the body with the square of the distance between the centroid and the point.

Fundamentals

Using the parallel axis theorem, the mass moment of inertia of a body about point O is determined as follows:

zpu + 1 = °1
…… (1)

Here, mass moment of inertia of the body about point is , moment of inertia of the body passing through the mass center is , mass of the body is and distance between the parallel axes is .

The formula to calculate the moment of inertia of a circular disc passing through the mass center is as follows.

1G.,dise =
m2
…… (2)

Here, mass of the circular disc is and radius of the circular disc is .

The formula to calculate the moment of inertia of a square plank passing through the mass center is as follows.

rain
…… (3)

Here, mass of the square plank is and length of the square plank is .

As the plate consists of two parts, it can be subdivided into two segments. Consider the circular part as segment and the square part as segment.

Show the schematic of segment of the thin plate as in Figure (1).

OSO
0.2 m
0.2 m
Figure 1

Calculate the mass of the segment 1.

m = ma,
m, = m(ar)

Here, mass per unit area of the thin plate is , area of the segment is and radius of segment is .

Substitute 20 kg/m²
for and for .

m. = (20 kg/m?)(x(0.2 m))
m = 2.513 kg

Calculate the moment of inertia of the segment passing through the mass center.

Substitute 2.513 kg
for and for .

19 = (2.513 kg)(0.2 m
16 = 0.05026 kg .m²

Calculate the mass moment of inertia of segment about an axis perpendicular to the page and passing through point.

¿pu+1 = 1

Here, distance between the parallel axes for segment is .

Substitute0.05026 kg.m?
for , 2.513 kg
for and for .

lg = 0.05026 kg. m’ +(2.513 kg)(0.2 m)
19 = 0.05026 kg • m² +0.10052 kg. m?
19 = 0.15078 kg. m
19 = 0.1508 kg. m?

Show the schematic of segment of the thin plate as in Figure (2).

0.2 m
0.2 m
0.2 m
1
Figure 2

Calculate the mass of the segment 2.

m = mA
m = m(c)

Here, area of the segment is and side of segment is .

Substitute for and for .

m2 = (20 kg/m²)(0.2 m)
m, = 0.8 kg

Calculate the moment of inertia of the segment passing through the mass center.I = sm
…… (4)

Here, diagonal length of the segment is .

Calculate the diagonal length of the segment .

r2 = (0.2 m)? +(0.2 m)
r= 0.08 m²
r2 = 0.2828 m

Substitute 0.8 kg
for and 0.2828 m
for in Equation (4).

19 = + (0.8 kg)(0.2828 m)
Io = 5.333x 10 kg. m²

Calculate the mass moment of inertia of segment about an axis perpendicular to the page and passing through point.

10 = 16+m,d

Here, distance between the parallel axes for segment is .

Substitute5.333x10-kg.m
for , for and for .

10x = 5.333x10-kg. m² +0.8kg)(0.2 m)
10= 5.333x10-? kg. m² +0.032 kg • m²
1o2 = 0.0373 kg-m?

Calculate the mass moment of inertia of the thin plate about an axis perpendicular to the page and passing through point .

1=1a-la

Substitute 0.1508 kg.m
for and 0.0373 kg.m
for .

16 = 0.1508 kg. m² -0.0373 kg.m?
16 = 0.1135 kg.m?

Ans:

The mass moment of inertia of the thin plate about an axis perpendicular to the page and passing through point is0.1135 kg.m
.

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