219
9-1 CE NTE R OF MASS
A
The com of the composite
plate is the same as the
com of the two pieces.
Plate P
2R
R
y
x
y
y
x
com P
com C
com S
Disk S
Composite plate
C = S + P
(a)
(b)
(c)
(d)
x
com P
com C
com S
Disk particle
Plate particle
Assume the plate's
mass is concentrated
as a particle at the
plate's center of mass.
Here too, assume the
mass is concentrated
as a particle at the
center of mass.
Here too.
Here are those
three particles.
Figure 9-4 (a) Plate P is a metal plate of radius 2R, with a circular hole of radius R. The center of mass of P is at point com P . (b) Disk S.
(c) Disk S has been put back into place to form a composite plate C. The center of mass com S of disk S and the center of mass com C
of plate C are shown. (d) The center of mass com SϩP of the combination of S and P coincides with com C , which is at x ϭ 0.