CHAPTER 5 PHYS 3080

Water settles to the bottom of a tank of gasoline. Which takes up more space: 1 kg of water or 1 kg of gasoline?

1 kg of gasoline because gasoline is less dense than water.

You are a deep sea diver and are carrying out pressure test son your air tanks, which is required by inspection rules. A gas cylinder is filled with a gas at a temperature of 300 K and pressure 200000 Pa. The temperature of the gas is then raised to 400 K. What is the new pressure?

266667 Pa

Water weighs about 10 N per liter. A 4.0 liter ball is pushed underwater. What is the buoyant force on the ball?

40 N

You are bored during the summertime when school is not in session and you decide to do an experiment where you compare the properties of water and air. If the density of air is 1.25 kg/m3 and the density of water is 1000 kg/m3 , what volume of air weighs the same as 1 liter of water?

800 liters

Water weighs about 10 N per liter. A 4.0 kg ball floats on the water's surface. What is the weight of the water being displaced by the ball?

About 40 N

Waterproof watches have a maximum depth to which they can safely be taken while swimming. Why?

Deeper than that depth the water pressure is so great it might damage the watch.

A helium-filled balloon floats in air. What will happen to an air-filled balloon in helium? Why?

It will sink because air is denser than helium.

A popular drink is composed by pouring several types of beverage (one on top of the other) in order to get a layering effect. In what order should the individual beverages be poured into the glass so that your drink is stable?

Most dense first and then in order of decreasing density.

If you seal a container of air at room temperature (20.0 ˚C) and then put it in the refrigerator (5.00 ˚C), what will the pressure inside the container be? Assume atmospheric pressure equal to 100,000. Pa.

P = 94883.16561 Pa

The particle density of standard atmospheric air at 288.15 K (15 ˚C) is 2.687x1025 particles/m3. Using the ideal gas law, calculate the pressure of this air.

P = ? Pa

If you seal a container of air at room temperature (20.0 ˚C) and then put it in the refrigerator (3.00 ˚C), what will the pressure inside the container be? Assume atmospheric pressure equal to 100,000. Pa.

P=94197.95221843003 Pa

Many jars have dimples in their lids that pop up when you open the jar. What holds the dimple down while the jar is sealed, and why does it pop up when the jar is opened?

The air outside is at higher pressure than the air inside the jar, which holds the dimple down. When the pressure equalizes, the dimple pops back to its normal position.

You seal a rigid container that is half full of hot food and put it in the refrigerator. Why is the container's lid bowed inward when you look at it later?

The air pressure of the air outside the container pushes the lid in.

Why must tall dams be so much thicker at their bases than at their tops?

The greater the depth of the water the greater the pressure pushing on the wall of the dam.

You can inflate a plastic bag by holding it up so that it catches the wind. Use Bernoulli's equation to explain this effect.

The kinetic energy of the moving air converts into greater air pressure inside the bag, which inflates the bag.

When you stand in a pool with water up to your neck, you find that it's somewhat more difficult to breathe than when you're out of the water. Why?

The pressure due to the depth of the water above your chest presses in on you

Each time you breathe in, air accelerates toward your nose and lungs. How does the pressure in your lungs compare with that in the surrounding air as you breathe in?

The pressure in your lungs is less than that of the surrounding air.

You are seated at a table in a Paris Café, contemplating life and watching the bubbles rise upward in your glass of carbonated water. You can think of many physical reasons why those carbon dioxide bubbles should rise upward through the water. Which of the follow observations is not true and therefore does not help explain why the bubbles rise in your Perrier?

The pressure inside a bubble is much less than the pressure in the water around it.

Many grocery stores display frozen foods in bins that are open at the top. Why doesn't the warm room air enter the bins and melt the food?

The warm air is blocked from the food by the cold air above the food.

For an object that is neutrally buoyant in a fluid,

The weight of the fluid displaced equals the object's weight.

Why must the pressure inside a whistle teakettle exceed atmospheric pressure before the whistle can begin to make noise?

The whistle is due to pressurized (greater than atmospheric pressure) steam forcing its way out through the narrow opening.

When a fish is floating motionless below the surface of a lake, what is the amount and direction of the force the water is exerting on it?

Upward, equal to the weight of the fish.

Suppose you have two containers with liquid in them. One has a density of 760 kg/m3 and the other has a density of 910 kg /m3. If an object floats in one container and sinks in the other, the density of the object

has a value between 760 kg/m3 and 910 kg/m3.

You are riding in a hot air balloon. You have not used the burner for some time and the balloon begins to sink. Assuming that no air is allowed to leave or enter the balloon,

the average density of the balloon became greater than the surrounding air and the buoyant force on the balloon became less than its weight

Suppose you have an aquarium and you notice that you have a solid plastic decoration and a rock of about the same volume but twice as dense, and both are totally submerged in the water. The buoyant force on the plastic object is about ___________as that on the rock.

the same.