Onondaga Community College Department of Chemistry and Physical Science
SCI 101 EXAM 1
Fall 2009
ONONDAGA COMMUNITY COLLEGE
DEPARTMENT OF CHEMISTRY AND PHYSICAL SCIENCE
sci 101: Physical sCIENCE i
Exam 2Fall2009
(65Points Total)
Name: ______Class Meeting Time___ __
Multiple Choice
Circle the BEST answer (25Points: 25 questions @ 1Pointeach)
1. Heat is the
A) total internal energy of an object.B) average kinetic energy of molecules.
C) measure of potential energy of molecules.
D) same thing as a very high temperature.
2. The specific heat of water is 1.00 cal/g°C and the specific heat of ice is 0.500 cal/g°C. The same amount of energy applied to equal masses, say 50.0 g of water and ice, will result in a greater temperature increase for the (assume the ice does not melt)
A) water.B) ice.
C) the same temperature increase for each.
D) unknown results.
3. The heat involved in the change of phase from solid ice to liquid water is called
A) latent heat of vaporization.B) latent heat of fusion.
C) latent heat of condensation.
D) none of the above.
4. The temperature of a gas is proportional to the
A) average velocity of the gas molecules.B) internal potential energy of the gas.
C) number of gas molecules in a sample.
D) average kinetic energy of the gas molecules.
5. Latent heat is "hidden" because it
A) goes into or comes out of internal potential energy.B) is a fluid (caloric) that cannot be sensed.
C) does not actually exist.
D) is a form of internal kinetic energy.
6. As a solid undergoes a phase change to a liquid, it
A) releases heat while remaining a constant temperature.B) absorbs heat while remaining a constant temperature.
C) releases heat as the temperature decreases.
D) absorbs heat as the temperature increases.
7. When you add heat to a substance, its temperature
A) always increases.B) sometimes decreases.
C) might stay the same.
D) might go up or down, depending on the temperature.
8. With all other factors being equal, the most likely to burn your mouth when taken directly from an oven is a food with
A) higher specific heat.B) lower specific heat.
C) specific heat is not important in this situation.
D) more information needed.
9. A large and a small container of water with the same temperature have
A) the same total amounts of internal energy.B) the same amounts of internal and external energy.
C) different amounts of heat.
D) the same amounts of all forms of energy.
10. A back and forth motion that repeats itself is a
A) spring.B) Vibration.
C) wave.
D) pulse.
11. The maximum displacement from rest to the crest or from rest to the trough of a wave is called
A) wavelength.B) period.
C) equilibrium position.
D) amplitude.
12. A wave with motion perpendicular to the direction that the wave is moving is classified as a
A) longitudinal wave.B) transverse wave.
C) water wave.
D) compression wave.
13. Sound waves with frequencies greater than 20,000 Hz are
A) infrasonic waves.B) supersonic waves.
C) ultrasonic waves.
D) impossible.
14. Generally, sounds travel faster in
A) solids.B) liquids.
C) gases.
D) vacuums.
15. Two sound waves of equal amplitude with slightly different frequencies will result in
A) an echo.B) the Doppler effect.
C) alternation of loudness of sound known as beats.
D) two separate sounds.
16. Longitudinal mechanical waves will move only through
A) solids.B) liquids.
C) gases.
D) All of the above are correct.
17. What comment is true about the statement that "the human ear hears sounds originating from vibrating objects with a frequency between 20 and 20,000 Hz"?
A) This is true only at room temperature.B) About 95 percent hear in this range, while some hear outside the average limits.
C) This varies, with females hearing frequencies above 20,000 Hz.
D) Very few people hear this whole range, which decreases with age.
18. What is changed by destructive interference of a sound wave?
A) frequencyB) phase
C) amplitude
D) wavelength
19. An airplane pilot hears a slow beat from the two engines of his plane. He increases the speed of the right engine and now hears a slower beat. What should the pilot now do to eliminate the beat?
A) Increase the speed of the left engineB) Decrease the speed of the right engine
C) Increase the speed of both engines
D) Increase the speed of the right engine
20. Resonance occurs when an external force matches the
A) interference frequency.B) decibel frequency.
C) beat frequency.
D) natural frequency.
D) standing waves.
21. The time required for one cycle of any repeating event is called one
A) hertz.B) period.
C) frequency.
D) amplitude.
22. A transverse wave causes particles of a material to move
A) back and forth in the same direction the wave is moving.B) perpendicular to the direction the wave is moving.
C) in a circular motion in the direction the wave is moving.
D) in a circular motion opposite the direction the wave is moving.
23. You hear a higher pitch when a sound wave has a greater
A) amplitude.B) velocity.
C) frequency.
D) wavelength.
24. The extent of displacement of a vibrating tuning fork is related to the resulting sound wave characteristic of
A) frequency.B) amplitude.
C) wavelength.
D) period.
25. During a track and field meet, the time difference between seeing the smoke from a starter's gun and hearing the "bang" would be less
A) on a warmer day.B) on a cooler day.
C) if a more powerful shell is used.
D) if a less powerful shell is used.
Short Answer Questions
(4 points each awarded based on completeness)
The kinetic theory of matter is a very successful theory because it successfully explains phenomena in several different fields of physics. Answer the questions below in a few sentences using the principles of the kinetic theory of matter and your knowledge of Heat and Waves Be certain to refer to principles of the kinetic theory of matter in each of your answers.
1)Sound waves travel more slowly in colder air than in warmer air. Why is this so?
The kinetic theory of matter states that all matter is comprised of particles that may or may not be bound together (depending on the phase of the matter) and are always in a constant state of motion. In a gas, the average kinetic energy () of the particles is a direct measure of the temperature of the gas. Cooler gases have particles with lower average kinetic energies. Thus, within a particular gaseous substance (m constant), colder implies slower molecules. Since a sound wave in a gas is propagated by molecules colliding into each other, a colder gas with slower molecules will propagate a disturbance (a wave) slower than a warmer gas.
2)The speed of sound in hydrogen gas is about four times faster than the speed of sound in air at the same temperature. Why is this so?
The kinetic theory of matter states that all matter is comprised of particles that may or may not be bound together (depending on the phase of the matter) and are always in a constant state of motion. In a gas, the average kinetic energy () of the particles is a direct measure of the temperature of the gas. In two gases, with different mass molecules, at the same temperature, the average kinetic energies of the molecules will be the same. However, in the gas with lighter molecules, the molecules will be moving faster, since kinetic energy = . If m is smaller in one gas then v will be larger in that gas. Since a hydrogen molecule is much lighter than a “air” molecule, the hydrogen molecules will be moving much faster than the air molecules even though both gases are at the same temperature. There average KE’s are equal, not their velocities. The faster molecules in the hydrogen gas will transmit a disturbance through the gas faster than the slower air molecules.
3)Steel has a speed of sound that is about three times faster that the speed of sound in lead. Why is that?
In solids, the kinetic theory of matter states that the particles that comprise the solid are bound together by chemical bonds that act like tiny springs coupling the motion of one molecule to its neighbors. Stronger chemical bonds act like “tighter springs”. The “tighter” the spring the more rapidly a disturbance is passed from one molecule to its neighbors. Weaker chemical bonds have molecules that are less strongly bonded to their neighbors and a disturbance at one molecule is passed to its neighbors less quickly. Steel is a very strong substance with strong chemical bonds and a high melting temperature (a measure of bond strength). On the other hand, Lead is a weak substance witht a low melting temperature (i.e weak bonds). Thus a disturbance on a steel molecule will be transmitted to its neighbors much faster than in lead. The speed of sound in solids does not depend on density, as can be seen in the Table of Sound Speeds.
4)When you stick your hand into a 450 F oven to remove a baking pan of food. The 450 F air in the oven does not burn your hand or ignite your sleeve or oven mitt. Why is this so?
The kinetic theory of matter states that all matter is comprised of particles that may or may not be bound together (depending on the phase of the matter) and are always in a constant state of motion. In a gas, the average kinetic energy () of the particles is a direct measure of the temperature of the gas. The sum of the kinetic energy of all the molecules in the gas represents the total internal energy (so long as we avoid phase changes). In a gas, that is a low density substance, there are far fewer molecules per unit volume than in a liquid or solid. Thus in a gas, the internal energy will be much less than in a equal volume of solid or liquid at the same temperature. This is best expressed in the heat equation . Since m is very small in a gas, the gas cannot contain much heat unless it is at a very high temperature. The air in the oven does not burn you because it contains very little heat energy. Notice, that air has a small specific heat (0.17 cal/gC), but metals typically have smaller specific heats. So It is not the small specific heat that prevents air burning you, but its low heat content due to its low mass per unit volume.
5)Heat continues to enter a boiling pot of water but it’s temperature does not change. Why is this so?
In liquids, the kinetic theory of matter states that the particles that comprise the liquid are weakly bound together by chemical bonds. As energy is added to a liquid, the kinetic energy of the molecules increases until the boiling point is reached. If more energy is added, that energy does not increase the kinetic energy of the molecules, but goes toward breaking the chemical bonds, allowing the liquid to become a gas. This energy is stored as internal potential energy and is related to the latent heat of vaporization. Only after the liquid is completely transformed into a gas will the KE of the molecules begin to increase and thus increase the temperature.
Problems
(20Points)
TO GET FULL CREDIT, YOU MUST SHOW ALLWORK
INCLUDING VARIABLES, EQUATIONS USED, UNITS, AND CONVERSIONS
1)A steel bar has a sound wave traveling through it with a frequency of 15,000 Hz. What is the wavelength of that sound wave in the steel? (4 points)
The wavelength of that sound wave in the steel is 39.6 cm.
2)100 grams of room temperature water (T=20C ) is placed into a freezer that will lower the temperature of the water to -10 C. How much heat must be removed by the freezer? (6 points)
The 100 g of water will be cooled through a phase change (liquid to solid). We need to compute three heat terms as illustrated above:
The heat that must be removed by the freezer is 10,500 calories.
3)A warm summer afternoon (T=32 C) thunderstorm produces lightning that you see 3 seconds before you hear the associated thunder clap. How far away is the thunderstorm? (4 points)
We first have to determine the speed of sound at this air temperature and then determine the distance.
The thunderstorm is 1,050 meters away.
This problem will ask you to apply the concepts of energy and heat to explore, very simply, the consequences of a large asteroid impact on the Earth’s oceans. All the parameters that are given below are realistic values.
4)An asteroid moving at 15 km/s has a diameter of 100 kilometers and a mass of 1.26x1019 kg. The asteroid impacts the Earth in the ocean. Assume that all the kinetic energy of the asteroid goes into heating all the Earth’s ocean water (this assumption is not that realistic but it provides an easy starting point for the problem.). The volume of Earth’s oceans is about 2.55x1018 m3 and the mass of the Earth’s oceans is about 3.19x1021 kg
A)Calculate the kinetic energy of the asteroid. (It will be a very large number). Express this energy in kcal. (3 points)
The KE of the asteroid is 3.39x1023 kcal.
B)Using the specific heat of seawater, calculate the temperature increase of the Earth’s oceans from their current average temperature of 4C , assuming all the KE went into heating the ocean water.(3 points) Answer on the bottom of the next page.
The ocean temperature would increase by 114 C, which would not be possible since this would put the temperature above the boiling point of water. Thus, the asteroid impact would cause the oceans to boil in this too simply represented situation.