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Solved problems for the chapter:

Pressure Changes

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Pressure in Fluids for A-Levels

1. Calculation of pressure in fluids

2. Air pressure

3. Devices operating on the basis of pressure in fluids

3.1. Connecting vessel

3.2. Measurement of liquid density

3.3. Siphon tube

3.4. Hydraulic press

3.5. Gas pressure gauge in a closed container

3.6. Air pressure gauge

4. Forum

↓ Show theory [1] ↓

Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:pressure_changes/3526/

Example 1.

A gas in a container is cooled but the volume of the gas does not change. Which row describes the changes in the pressure of the gas and the average kinetic energy of the gas particles?

	pressure of gas	average kinetic energy of gas particles
A	decreases	decreases
B	decreases	increases
C	increases	decreases
D	increases	increases

Example 2.

A sample of gas is trapped in a rigid container. As the temperature of the gas is increased, the pressure increases. Which statement is not correct?

The gas molecules have greater kinetic energy.
The gas molecules hit the walls of the container harder.
The gas molecules hit the walls of the container more frequently.
The gas molecules move further apart.

A piston traps a mass of gas inside a cylinder. Initially, the piston is halfway along the length of the cylinder. The piston is now moved towards the open end of the cylinder. The temperature of the gas remains constant.

How are the density and the pressure of the gas affected by moving the piston?

	density	pressure
A	decreases	decreases
B	decreases	unchanged
C	increases	decreases
D	increases	unchanged

A fixed mass of gas is trapped in a container. The temperature of the gas is increased but the volume of the gas is kept constant. How does this change affect the average kinetic energy of the molecules and the pressure on the walls of the container?

	average kinetic energy	pressure
A	increases	increases
B	stays the same	increases
C	increases	decreases
D	decreases	increases

The pressure of a fixed mass of gas in a cylinder is measured. The volume of the gas in the cylinder is slowly decreased. The temperature of the gas does not change. Which graph shows how the pressure of the gas changes during this process?

The temperature of the gas in a sealed container of constant volume decreases from to . Which row is correct?

	pressure of the gas in the container	average speed of the molecules of gas
A	increases	increases
B	increases	stays the same
C	stays the same	decreases
D	decreases	decreases

The figure below shows two cylinders connected by a narrow tube fitted with a tap.

One cylinder contains of gas at a pressure of . The other cylinder contains a vacuum. The volume of the evacuated cylinder is . The tap is opened so that the gas can flow to fill both cylinders. The temperature of the gas remains constant. What is the new pressure of the gas?

The figure below shows a sealed gas cylinder with a movable piston.

The piston is moved slowly downwards and there is no change in the temperature of the gas. What happens to the average distance between the gas molecules and the pressure of the gas?

	average distance between gas molecules	pressure of gas in cylinder
A	increases	decreases
B	decreases	increases
C	decreases	decreases
D	increases	increases

The same mass of a gas is trapped in four identical cylinders by a piston that can move. The diagrams show the samples of gas in different conditions of volume and temperature.

Which list gives the pressure of the gas in order from lowest to highest?

10.

The relationship between pressure and volume of a gas is given as . Under which conditions for the mass of a gas and for its temperature does the equation hold?

	mass	temperature
A	changing	changing
B	changing	constant
C	constant	changing
D	constant	constant

11.

A car tyre contains air. The temperature of the air in the tyre rises. The volume of the air in the tyre remains constant. Students are asked to suggest how this temperature rise will affect the movement of the air molecules.

The air molecules will move faster.
The air molecules will hit the tyre walls more often.
The air molecules will hit the tyre walls harder.

Which suggestions are correct?

1, 2, and 3
1 and 2 only
1 and 3 only
2 and 3 only

12.

A sealed box contains a fixed mass of gas. Which action results in each molecule of the gas colliding with the walls of the container less frequently and with a smaller force?

Increase the volume of the container.
Increase the temperature of the gas.
Decrease the volume of the container.
Decrease the temperature of the gas.

13.

Air in a sealed syringe is slowly compressed by moving the piston. The temperature of the air stays the same.

Which statement about the air is correct?

The pressure of the air decreases because its molecules now travel more slowly.
The pressure of the air increases because its molecules now hit the syringe walls more frequently.
The pressure of the air decreases because the area of the syringe walls is now smaller.
The pressure of the air increases because its molecules now travel more quickly.

14.

On a warm day, a driver checks the air pressure in a car tyre. At night, the temperature drops and the air pressure in the tyre decreases. There are no air leaks in the tyre. Why does the pressure decrease?

The air molecules in the tyre move more slowly.
The volume of the air in the tyre decreases.
The volume of the air in the tyre increases.
The air molecules in the tyre stop moving.

15.

A gas bubble is formed deep under water. The bubble has a volume of and the pressure inside the bubble is . The bubble rises up through the water. The volume of the bubble increases to and the pressure becomes . The temperature of the gas does not change. What is the initial pressure ?

16.

A sealed bottle of constant volume contains air. The air in the bottle is heated by the Sun. What is the effect on the average speed of the air molecules in the bottle, and the average distance between them?

	average speed of air molecules	average distance between air molecules
A	decrease	decrease
B	decrease	stays the same
C	increase	increase
D	increase	stays the same

17.

The diagram shows a quantity of gas enclosed in a cylinder by a piston.

The piston is moved to the left or to the right. The temperature of the gas is kept constant. Which row describes the effect of moving the piston slowly in the direction shown in the table?

	movement of piston	speed of gas molecules	pressure of gas
A	to the left	increases	decrease
B	to the left	no change	increases
C	to the right	increases	decreases
D	to the right	no change	increases

18.

The diagram shows a quantity of gas trapped in a cylinder. The piston is pushed in slowly and the gas is compressed. The temperature of the gas does not change.

Which graph shows the relationship between the pressure and the volume of the gas?

19.

The figure below shows some gas, at room temperature, in a cylinder with a piston that can move. The gas

cannot escape from the cylinder.

Describe how the gas particles exert a pressure on the walls of the cylinder and piston.
The piston in the figure moves to the left. The volume of the gas decreases. The temperature of the gas does not change. State and explain any change in the pressure of the gas when the piston moves to the left.

20.

Some gas is trapped in a cylinder fitted with a moveable piston. The figure below shows the arrangement.

Describe how the gas exerts a pressure on the cylinder. Use your ideas about molecules.
The piston moves and increases the volume occupied by the gas. The temperature of the gas remains constant. The figure below shows the new position of the piston.

State and explain what happens to the pressure of the gas on the cylinder.