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Practice Problems 0. Here is a set of old test questions covering these same topics, in multiple-choice format. 1D, 2C, 3A, 4D, 5B, 6B, 7C, 8E, 9C, 10B, 11E 1. Why does the buoyant force happen? Circle one choice in each set
of brackets: Pressure {increases, decreases} the deeper down in a fluid.
If an object is submerged in the fluid, the pressure pushing {up, down}
on the {bottom, top} of the object is {greater, less} than the pressure
pressing {up, down} on the {bottom, top} of the object. (Or, you can reverse the choice in every set of brackets, except the first.) 2. Look at the table of desities given on the "Density"
notes page. What item or items listed there would float in mercury? All of them, except gold. 3. In about five billion years, the Sun will run out of
the hydrogen fueling its nuclear reactions. After going through
a "red giant" phase, gravity will cause the Sun to shrink
down to about the size of the Earth, forming a dead star known
as a "white
dwarf".
What will be the density of the white dwarf, in g/cm³. Assume
the mass of the sun (2x1030 kg) collapses into a sphere
6000 km in radius. 2.2 million g/cm³. 4. A solid steel ball is floating in mercury. What percentage of the
ball is sticking up above the surface of the mercury? The ratio of their densities is 7.9/13.6 = 58% below the surface, therefore 42% is above the surface. 5. Most people have a density about the same as water --- let's say
your density is the same as water. If your mass is 50
kg, then... 6. The strength of gravity (g) at the surface of Europa, one
of Jupiter's moons, is 1.32 N/kg. Europa has a thin water ice crust
(perhaps
20km thick) below
which lies a liquid water ocean that could be as deep as 200 km. What is the pressure at the bottom of this
ocean? (Assume g doesn't vary significantly over that depth.) Calculate density * g * h for both the ice layer and the water layer, then add those pressures together to yield 2.88e8 Pa, which is the same as 2850 atmospheres. 7. A solid ball floats in water, but sinks when immersed in vegetable oil. What can you say about the density of the ball? It must be less dense than water, but more dense than the oil. So the density must be between 925 and 1000 kg/m³ 8. A block is 10 centimeters tall. When floating in a bowl of mercury, 4 centimeters is below the surface of the fluid. What is the density of the block? 5.4 g/cm³ 9. Is a spherical helium balloon 5.0 meters in diameter big enough to lift a person? The density of air near the ground is 1.25 kg/m³. The density of helium at one atmosphere pressure is 0.18 kg/m³. 10. A uniform beam of length 1.8 m and mass 55 kg is suspended by two chains hanging vertically. The left chain is attached to the beam 20 cm from the left end, and the right chain is attached 50 cm from the right end. What is the tension in each of the chains? 196 N for the left chain, and 343 N for the right chain 11. If water comes out of a particular garden hose (diameter 5/8") at 1.90 m/sec... Note 5/8" = 15.9 mm = 0.0159 m and that means a cross-sectional area of 1.98x10-4 m2.
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