Q: A 100 kg person stands on a frozen pond with an area of contact of $$0.0100\,m^2$. What is the pressure exerted on the ice? (Assume g = 9.80$$\,m\,$$s^{-2})$$

$$P = \frac{F}{A} = \frac{100\,kg \times 9.80\,m\,s$$^{-2}$$}{0.0100\,m^2$} = 9,800\,Pa$$

Q: Convert a pressure of $$750.0\,mmHg to$$ $$kPa. (1 $$atm = 101.3 kPa, 1 atm = 760 mmHg)

$$750.0\,mmHg \times \frac{101.3\,kPa}{760\,mmHg} = 99.99\,kPa$$

Q: A manometer is used to measure the pressure of a gas in a container. If the atmospheric pressure is $$101.3\,kPa$$ and the mercury level on the gas side is $$20\,mm$$ higher than the open side, what is the pressure of the gas in $$kPa$$? (Assume $$1\,mmHg = 0.133\,kPa)$$

$$101.3\,kPa + (20\,mm \times 0.133\,kPa/mm) = 103.96\,kPa$$

Q: A car of mass $$1500\,kg$$ comes to a stop from $$50\,km\,h$$^{-1}$$ in 2$$\,s$$ against a wall. If the contact area is 0.25$$\,$$m^2$$, what is the average pressure exerted on the wall? ($$1\,km\,h$$^{-1}$$ = 0.278\,m\,s$$^{-1}$$)

$$P = \frac{F}{A} = \frac{1500\,kg \times \frac{(0 - 13.89)\,m\,s$$^{-1}$$}{2\,s}}{0.25\,m^2$} = 41,670\,Pa$$

Question 1

Which of the following best explains why gas pressure increases when the temperature of a gas is increased in a sealed, rigid container?

Accepted Answer

The gas molecules move faster, increasing both the frequency and force of collisions with the container walls.

Question 2

A 100 kg person stands on a frozen pond with an area of contact of $$0.0100\,m^2$. What is the pressure exerted on the ice? (Assume g = 9.80$$\,m\,$$s^{-2})$$

Accepted Answer

$$P = \frac{F}{A} = \frac{100\,kg 	imes 9.80\,m\,s$$^{-2}$$}{0.0100\,m^2$} = 9,800\,Pa$$

Question 3

Which of the following is the correct relationship for pressure in terms of force and area?

Accepted Answer

$$P = \frac{F}{A}$$

Question 4

A gas cylinder contains nitrogen gas at $$10^\circ C$$ and $$1.25\,g\,L$$^{-1}$$. What is the volume occupied by 1 mole of nitrogen gas under these conditions? (M_N = 28.02$$\,g\,$$mol^{-1})$$

Accepted Answer

$$V = \frac{28.02\,g\,$$mol^{-1}$$}{1.25\,g\,L$$^{-1}$$} = 22.4\,L$$

Question 5

Which of the following units is NOT a standard unit of pressure?

Accepted Answer

joule

Question 6

At the bottom of the Mariana Trench, the pressure is $$1086\,bar. If $$standard atmospheric pressure at sea level is $$1\,bar$$, how many times greater is the pressure at the bottom of the trench compared to sea level?

Accepted Answer

About 1086 times greater

Question 7

A barometer is used to measure atmospheric pressure. What physical principle allows the barometer to function?

Accepted Answer

Atmospheric pressure pushes the liquid up the tube until it balances the weight of the liquid column.

Question 8

Which of the following best describes why a sharp ice skate blade exerts more pressure on ice than a flat shoe of the same mass?

Accepted Answer

The blade has a smaller area, so the same force is concentrated over a smaller area, increasing pressure.

Question 9

Convert a pressure of $$750.0\,mmHg to$$ $$kPa. (1 $$atm = 101.3 kPa, 1 atm = 760 mmHg)

Accepted Answer

$$750.0\,mmHg 	imes \frac{101.3\,kPa}{760\,mmHg} = 99.99\,kPa$$

Question 10

A manometer is used to measure the pressure of a gas in a container. If the atmospheric pressure is $$101.3\,kPa$$ and the mercury level on the gas side is $$20\,mm$$ higher than the open side, what is the pressure of the gas in $$kPa$$? (Assume $$1\,mmHg = 0.133\,kPa)$$

Accepted Answer

$$101.3\,kPa + (20\,mm 	imes 0.133\,kPa/mm) = 103.96\,kPa$$

Question 11

Which of the following factors does NOT directly affect the pressure exerted by a gas in a closed container?

Accepted Answer

The color of the container

Question 12

A car of mass $$1500\,kg$$ comes to a stop from $$50\,km\,h$$^{-1}$$ in 2$$\,s$$ against a wall. If the contact area is 0.25$$\,$$m^2$$, what is the average pressure exerted on the wall? ($$1\,km\,h$$^{-1}$$ = 0.278\,m\,s$$^{-1}$$)

Accepted Answer

$$P = \frac{F}{A} = \frac{1500\,kg 	imes \frac{(0 - 13.89)\,m\,s$$^{-1}$$}{2\,s}}{0.25\,m^2$} = 41,670\,Pa$$

Question 13

Which of the following statements about gas pressure is TRUE?

Accepted Answer

Gas pressure results from the collisions of gas molecules with the surfaces of their container.

Question 14

If the density of a liquid nitrogen sample at $$77\,K is$$ $$0.808\,g\,mL$$^{-1}$$, what is the volume occupied by 1$$\,mol$$ of liquid nitrogen? (M_N = 28.02$$\,g\,$$mol^{-1})$$

Accepted Answer

$$V = \frac{28.02\,g}{0.808\,g\,mL$$^{-1}$$} = 34.7\,mL$$

Question 15

Which of the following is the correct conversion between $$1\,atm$$ and $$mmHg$$?

Accepted Answer

$$1\,atm = 760\,mmHg$$

Question 16

A gas sample is collected over water at $$25^\circ C$$ and the atmospheric pressure is $$760\,mmHg. If $$the vapor pressure of water at $$25^\circ C is$$ $$24\,mmHg$$, what is the pressure of the dry gas?

Accepted Answer

$$760\,mmHg - 24\,mmHg = 736\,mmHg$$

Question 17

Which of the following best describes why the pressure at the bottom of the Mariana Trench is so much greater than at sea level?

Accepted Answer

The weight of the water column above exerts a much greater force per unit area.

Chapter 5.1 : Gases – Pressure, Measurement, and Units

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