C.8 An empty boat is placed in a freshwater lake and a mark is painted on the hull at the waterline, a line corresponding to the
surface of the water when the vessel is floating upright. The same boat is then transported to Jupiter, and placed into a pool
of fresh water that has been prepared just for this comparison experiment. The acceleration due to gravity on Jupiter is 2.6
times what it is on Earth. The new waterline is noted on Jupiter. Compared to the waterline mark on Earth, where is the new
waterline mark located on the hull of the boat? Ignore atmospheric effects.
The new waterline mark is i. higher
ii. lower
iii. at the same placeon the hull.C.9 An empty boat is placed in a freshwater lake and a mark is painted on the hull at the waterline, a line corresponding to the
surface of the water when the vessel is floating upright. The boat is then transported to the Dead Sea, where the liquid density
is about 1.2 times that of fresh water due to the high concentration of salts. A waterline mark is noted in the Dead Sea.
Compared to the first waterline mark, where is the new waterline mark located on the hull of the boat?
The new waterline mark is i. higher
ii. lower
iii. at the same placeon the hull.C.10You hold a ping-pong ball and a steel ball bearing of the same diameter so that they are submerged underwater. Which one
experiences the greater buoyant force? Explain your answer.
i. The ping-pong ball
ii. The ball bearing
iii. The buoyant forces are the same
.C.11A ping-pong ball and a steel ball bearing of the same diameter are thrown into a swimming pool. The ball floats, while the
bearing sinks. Which one experiences the greater buoyant force? Explain your answer.
i. The ping-pong ball
ii. The ball bearing
iii. The buoyant forces are the sameC.12A boat carrying a load of bricks is floating in a canal lock. One of the crew members throws a brick overboard, and it sinks.
Does the level of the water in the lock rise or fall? Explain your answer.
It rises It fallsC.13Explain how you would float a battleship in a thimbleful of water. This is a real question, not a trick question, except that you
have to make one idealizing assumption: Water does not consist of discrete molecules, but is a "fluid" at every scale of
magnitude.
C.14Susie is out fishing on a calm, sunny day. She hooks an old tire that is resting on the lake bottom, and hauls it into her boat.
In principle, how does the water level of the lake change?
The lake's water level i. drops very slightly
ii. does not change
iii. rises very slightlyC.15Susie is out fishing again on another calm, sunny day. She sees a chunk of firewood floating in the water, and hauls it into
her boat. In principle, how does the water level of the lake change?
The lake's water level i. drops
ii. does not change
iii. risesC.16Here is a trick that is often performed as a physics demonstration. A vacuum cleaner hose and wand are attached to the
"back end" of a canister-type vacuum cleaner so that the wand directs a fountain of air straight upward. Then a light ball is
placed on top of the fountain where it bobs around and even tumbles to the side, but always returns to the top of the fountain
without actually falling off. Explain how this trick works.
C.17People are warned not to stand near open doors on airplanes in flight, because they can get "sucked" out of the door. Explain
how this might happen.
Section Problems
Section 2 - Density
2.1 Calculate the average population density in people/km^2 for each of the following geopolitical entities. (a) The United States,
whose population is 293×10^6 people, and land area is 9.37×10^6 km^2. (b) The world, whose population is 6356×10^6 people,
and land area is 149×10^6 km^2. (c) Siberia, whose population is 25.1×10^6 people, and land area is 13.5×10^6 km^2. (d) Hong
Kong, whose population is 6.70×10^6 people, and land area is 1098 km^2.