Oregon State University
Physics 202
,
Winter 2010
HW12 (due Jan 15 at 5:00 p.m.)
Page
1
Oregon State University
Physics 202
Winter Term,
2010
HW12
Note:
This HW assignment, due January 15, covering
topics—mixed freely—from Chapter
o
1
r
3 of the text.
Of these problems,
only two will be scored (for a possible 20 points).
Donʼt forget the extra credit point that is available, too—see the course
web site, under the links for recitation/Homework (HW).
/
These problems are presented in no particular order and may freely
use/mix concepts throughout the assigned sections of Chapter 13.
Follow the recommended format for problem solutions, use
SI units unless directed otherwise, and assume three significant digits in all numerical answers.
1.
Pure water and then oil (which donʼt mix) are poured into a Ushaped tube,
open at both ends.
The liquids come to equilibrium as shown here.
What is the oilʼs density?
2.
A raft is made of 12 identical logs lashed together.
Each log is 36.0 cm
in diameter,
7.25 m long, and has a density of 750 kg/m
3
. How many 60kg persons can the raft
hold (ﬂoating in pure water) while still keeping everyoneʼs feet dry?
3.
Using Archimedesʼ Principle and the labels and diagram shown here:
(a)
prove that if an object is ﬂoating in a liquid,
the fraction of the
objectʼs total volume that is
immersed (below the surface)
is the ratio of its density (
ρ
obj
) to the liquidʼs density (
ρ
liq
);
(b)
prove that when ice melts in a glass of water,
the water level does not change.
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 Spring '08
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 Physics

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