Posted by **James** on Saturday, June 16, 2012 at 9:50pm.

5. A circular pizza of radius R has a circular piece of radius R/3 removed from one side. The center of mass of the pizza with the hole is at a distance of_____ from the center of mass of the original pizza.

A. R/20

B. R/2

C. R/30

D. R/3

E. R/12

The answer is E, but why is it E? Thank you in advance.

- Physics -
**Damon**, Saturday, June 16, 2012 at 10:02pm
say mass is area (density would cancel)

original mass = pi R^2 with center at x = 0

mass of cutout = pi R^2/9 with center at x = (2/3)R

mass of remaining = 8 pi R^2/9 with center at x

8 pi R^2/9 * x + pi R^2/9 * 2R/3 = pi R^2 * 0

8 x = - 2 R/3

x = - R/12 yes E

- Physics -
**James**, Saturday, June 16, 2012 at 10:14pm
How is it known that the mass of the cutout is centered at (2/3)R?

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