Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

9.6 Momentum 239

Thin Rectangular Plate

Izz (9.13)

1

12

mW

2

W

z

z

Example 9.1 Determine the mass moment inertia of a steel shaft that is 2 m long and has a diameter (d) of

10 cm. The density of steel is 7860 kg /m

3

We will first calculate the mass of the shaft using Equation (9.1). The volume of a cylin-

der is given by

To calculate the mass moment of inertia of the shaft about its longitudinal axis, we use

Equation (9.11).

9.6 Momentum

Mass also plays an important role in problems dealing with moving objects.Momentumis a

physical variable that is defined as the product of mass and velocity.

L (9.14)

!

mV

!

Izz

1

2

mR

2



1

2

1 123.5 kg 21 0.05 m 2

2

0.154 kg#m

2

mass123.5 kg

7860 kg/m

3



mass

0.01571 m

3

density

mass

volume

volume 1 p/4 21 d

2

21 length 2  1 p/4 21 0.1 m 2

2

1 2 m 2 0.01571 m

3

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