Formulas and Constants. F = ma w = mg. Q = ml f. Q = ml v. W = F d. P = W t. PE = mgh E = KE + PE. v = λf. v = [ T ] m s

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1 PHYS 1400: PHYSICAL SCIENCE FOR GENERAL EDUCATION SPRING 2018 Name: Exam 02: Chapters Instructions Put your name on this test paper. When you complete the exam, the test paper must be submitted. This exam paper will be returned to you when it is graded. You may use your calculator and the formula sheet provided. You may not use your phone or any additional reference materials. Respond to each question using your clicker. Remember, only SUBMIT your answers after you have double-checked, and are satisfied with your responses. Clicking SUBMIT is the same as handing in your test paper, and you may not alter your responses after you submit them. Make sure that your phone is switched off. It should be put away, and nowhere visible on your desk. If your phone rings during the exam, you will be required to turn in your exam and leave the room. You will not be allowed to return and complete any unfinished portions of the exam. You may not use any type of mobile device as a calculator. Mark your answers on the test paper as well as clicking. Exams will not be scored by hand, but you definitely want a record of your responses in case some catastrophe strikes my laptop. There is exactly one correct answer for each question. Each question is worth 2 points. There is no partial credit. Formulas and Constants Acceleration due to gravity: g = 9.8 m s 2 Newton #2: Weight: F = ma w = mg Specific heat brass: Specific heat iron: Specific heat of tin: Specific heat of lead: cbr = cal/g C cfe = cal/g C csn = cal/g C cpb = cal/g C Law of Gravity: F = G m 1 m 2 r 2 Work: W = F d Heat to change phase (solid liquid): Heat to change phase (liquid gas): Q = ml f Q = ml v Power: P = W t Kinetic Energy: KE = 1 2 mv 2 Gravitational Potential Energy: Total Energy: Work Energy Theorem: Work Energy (general): Heat to change temperature: Specific heat water: Specific heat aluminum: Scoring Each question is worth 2 points. PE = mgh E = KE + PE 1 2 mv2 i + W = 1 2 mv2 f Q = mc( ΔT) cw = 1 cal/g C cal = cal/g C Latent heat of fusion (water): Latent heat of vaporization (water): Hooke s Law: Wave frequency: Wave speed: Distance equation: Speed of sound in air: Speed of sound in water: Range of audible frequencies: Lf = 80 cal/g Lv = 540 cal/g F = kx v = λf v = [ T ] m s v = 1530 m/s 20 Hz f 20kHz Score: /100

1. In the context of physics, energy is A) a process: an object can do/perform energy. B) a property: an object can have/possess energy. C) a constant: all objects contain equal energy. D) a mystery.

2 1. In the context of physics, energy is A) a process: an object can do/perform energy. B) a property: an object can have/possess energy. C) a constant: all objects contain equal energy. D) a mystery. Physicists have no idea how energy works. 2. A tennis ball is held above the ground as shown on the right. You raise the the ball from position A to position B. Using the ground as your reference level, compare the work done by gravity and the potential energy. A) Gravity does positive work on the ball, and the potential energy at B is greater than the potential energy at A. B) Gravity does positive work on the ball, but PEB is smaller than PEA. C) Gravity does negative work on the ball, and PEB is greater than PEA. D) Gravity does negative work on the ball, and PEB is smaller than PEA. 3. Which of the following is not a form of potential energy? h=0 A) Gravitational. D) Spring (or elastic). B) Electrical. E) All these are examples of C) Magnetic. forms of potential energy! 4. True or false: An object may have either positive or negative potential energy. 5. True or false: An object may have either positive or negative kinetic energy. 6. Calculate the kinetic energy of a 125 lb (m = 57 kg) skier moving at 20mph (v = 9.0 m/s). Answer numerically (do not include any units). 7. True or false: The skier converts chemical energy (breakfast!) into mechanical energy (skiing!). 8. As the skier slaloms downhill, her speed increases. If the skier is speeding up, A) kinetic energy is being converted into gravitational potential energy. B) gravitational PE is being converted into KE. C) kinetic energy is increasing for some unknown reason. There is no exchange betweenke and PE. 9. You throw a tennis ball vertically, straight up in the air, with some initial velocity vo. As the ball rises, A) its KE increases while its PE decreases. B) its KE decreases as its PE increases. C) KE and PE both remain constant. D) both KE and PE decrease. E) KE and PE both increase. hb ha 10. In the context of physics, what do we mean by conservation of energy? A) Energy is continually created, but without careful conservation, it will be easily destroyed. B) Energy cannot be created, so unless it is carefully conserved, it will be destroyed, leaving nothing. C) Energy cannot be created or destroyed; it can only be transferred from one object to another, or transformed from one type of energy to another. D) Energy cannot be created or destroyed. It cannot be transferred from one object to another, and it definitely cannot change form (like from electrical to mechanical). 11. Distinguish between an atom and a molecule. A) An atom is a single particle (like hydrogen). When two or more atoms are joined, it becomes a molecule (like water = H 2O = 2 hydrogen atoms + 1 oxygen atom). B) An atom is the smallest particle of a solid, while a molecule is the smallest particle of a liquid or gas. C) An atom is a group of ten particles bonded together. Molecules are larger, and consist of 1 million particles bonded into a single unit. D) Technically, answer A is correct. However, for the purposes of Kinetic Theory, we can refer to either atoms or molecules as molecules. 12. Which of the following is an example of cohesion? A) Using masking tape to seal a moving box. B) Using a weird rubbery material to suspend a car upside down from the ceiling. C) Observing dewdrops on the grass in the morning. D) Using a magnet to display a photo on the fridge. E) All of these, except answer C! 13. Of the three phases of matter (solid, liquid, gas), which one demonstrates the weakest cohesive bonding between molecules? A) Solids. B) Liquids. C) Gases. D) Trick question. Cohesive strength does not depend on the phase of the matter; it s the same for all phases. 14. If both liquids and gases are fluids, what is the difference between them? A) Liquids are made of molecules, while gases are made up of atoms. B) A liquid has fixed volume, but variable shape. Gases have both variable volume and shape. C) A liquid has almost zero cohesive bonding between molecules, while gases have strong cohesive bonds. D) All of these answers are accurate! 15. True or false: The molecules of a solid material may seem stationary, but they are continuously in motion. 16. Which of the following is not an example of molecular motion by diffusion? A) A drop of food coloring gradually turns an entire glass of water red. B) You can smell dinner cooking in the kitchen even if you are down the hall and in your bedroom. C) Boiling water poured over herb leaves in a mug results in a delicious cup of tea. D) You light a candle and the wax melts into a liquid pool surrounding the wick. EXAM 02 PAGE 02

E) the energy transferred from one substance to another because of a temperature difference. 18.

3 17. Temperature is defined as A) the average heat of an object. B) the average chemical potential energy per molecule of a substance. C) the average gravitational potential energy per molecule of a substance. D) the average internal kinetic energy per molecule of a substance. E) the energy transferred from one substance to another because of a temperature difference. 18. When you decrease the temperature of a substance, the individual molecules will A) move faster, get farther apart, and occupy more space. B) move faster, get closer together, and occupy a smaller volume. C) move slower, get closer together, and occupy less space. D) move slower, slowly drift apart, occupy a greater volume of space. 19. You have two identical cups of fresh, hot coffee, both sitting on the counter. Cup A has a thermometer in it which reads 185, and Cup B has a thermometer reading 72. The temperature scales are not labeled, but which one must be calibrated with Celsius degrees? A) Thermometer A. B) Thermometer B. 20. What is the difference between the Celsius and Kelvin temperature scales? A) There is no difference whatsoever between them. B) Degrees Celsius are larger than degrees Kelvin. C) 0 K is much warmer than 0 C. D) Celsius is a relative scale is based on the freezing and boiling of water; Kelvin is an absolute scale. 21. True or false: A welding spark, while having a very high temperature, actually contains very little heat. 22. True or false: A swimming pool filled with water at 20 C contains far less heat than a welding spark at 5000 C. 23. Two metal bars are brought into contact, end to end. One bar has a temperature of 0 C, and the other is at 50 C. A) Heat is exchanged in both directions, from hot to cold and from cold to hot until both bars reach the same final temperature. B) The cold bar gives energy to the hot one until it comes down to 0 to match the cold one. C) The hot bar transfers heat to the cold one until both reach a final temperature between 0 and 50. D) No heat is transferred in either direction, since metal is a very poor conductor of heat. 24. True or false: Metals generally have very high specific heats when compared to the specific heat of water. 25. How much energy (Q, in calories) is required to raise the temperature of 10g of water from very cold (Ti = 3 C) to room temperature (Tf = 22 C)? A) Q = 10cal C) Q = 19cal E) Q = 190cal B) Q = 17cal D) Q = 170cal F) Q = 250cal The cylinders shown on the right all have precisely the same mass. They are all heated to 100 C, then placed on the block of wax as shown. Each cylinder melts the wax until it reaches room temperature (20 C). Use the multiple choices shown on the figure to answer Question The cylinders shown are brass, iron, lead, and tin. Identify which cylinder is tin. C = tin (second lowest specific heat) 27. Conduction is A) the transfer of heat between objects that are not actually touching. B) the transfer of heat via bulk motion of the medium. C) the transfer of heat by electron and atomic collisions. D) the only way to transfer heat from a colder object to a warmer one. 28. Convection is A) the transfer of heat via bulk motion of the medium. B) the transfer of heat by electron and atomic collisions. C) the transfer of heat between objects that are not actually touching. D) the only way to transfer heat from a colder object to a warmer one. 29. An ice cube tray is filled with liquid water at room temperature (about 20 C) and placed in the freezer. A) The temperature won't decrease, staying at 20 C, until all the water has frozen into ice. B) The water temperature decreases to the freezing point (0 C) before the phase changes. Once the ice freezes, then the temperature can then be decreased more. C) The temperature goes down by half, then half the water freezes. The temperature of the remaining water goes down by half again, then half of the liquid freezes. This pattern repeats until all of the liquid has changed phase. D) The process is totally random, so the temperature decreases and phase changes or not. You can't ever predict what will happen, only the final result: solid ice. 30. The specific heat of water is c = 1 cal/g C, and the the latent heat of vaporization is Lv = 540 cal/g. You have 10g of warm water initially at 45 C. How much total energy (Q) must be added to completely vaporize all of the water? A) Q = 1 cal/g C cal/g + 10 g + 45 C = 596cal B) Q = 540 cal/g + (100 45) C = 595cal C) Q = (10g)(1cal/g C)(45 C)+(10g)(540cal/g) = 5850cal D) Q = (10g)(1cal/g C)(100 45) C+(10g)(540cal/g)=5950cal A B C D EXAM 02 PAGE 03

4 31. Evaporation of a liquid is a cooling process. This means that A) the higher energy liquid molecules escape, leaving the lower energy molecules behind. B) the lower energy liquid molecules collide with and stick to a cooler surface, and cool that surface. C) the higher energy molecules give their energy to the lower energy molecules, lowering the average energy and thus the temperature of the liquid. D) all of the liquid molecules have the same energy; it is a cooling process because you have to put the liquid in the refrigerator (or some kind of cooler) in order to start the evaporation process. 32. True or false: Steel is an example of a very elastic material. 33. A wave is A) an oscillation in time only. B) an oscillation in space only. C) an oscillation in space propagated through time. D) an oscillation in time propagated through space. 34. True or false: As a wave propagates, the medium is carried along, also propagating in the same direction. 35. The sweep hand of a stopwatch completes one full revolution (or cycle) each minute (60 seconds). A) Its frequency f = 60 Hz, and its period T = 1 sec. B) Its frequency f = ( 1 /60) Hz, and its period T = 60 sec. C) Its frequency f = 1 Hz, and its period T = 1 sec. D) Its frequency f = 60 Hz, and its period T = ( 1 /60) sec. Answer Questions using the wave diagram below. If a numeric response is required, respond with exactly two decimal places (no units!) y (m) 0.20 A B Identify points A, B, and C on the figure above. A) A: trough; B: node; C: crest. B) A: node; B: trough; C: crest. C) A: crest; B: trough; C: node. D) A: trough; B: crest; C: node. 37. What is the amplitude of this wave? A = 0.40m 38. What is the period of this wave? T = 0.8s 39. What is the frequency of this wave? f = 1/T = 1.25Hz C t (s) 40. If the wavelength of the above wave is measured to be λ = 2.8m, what is the wave speed (remember that v = λf)? v = λf = (2.8m)(1.25Hz)=3.5 m /s A) v = 0.17 m/s C) v = 2.5 m/s E) v = 5.0 m/s B) v = 2.24 m/s D) v = 3.5 m/s F) v = 6.0 m/s 41. A transverse wave propagates A) parallel to the direction of the oscillation. B) perpendicular to the direction of the oscillation. C) neither parallel nor perpendicular to the propagation. D) not at all. Transverse waves only oscillate (while longitudinal waves only propagate). 42. True or false: Seismic waves may be either longitudinal or transverse. 43. For a sound to be audible to an average human, it must have A) a frequency between Hz and 1Hz. B) a frequency between 20Hz and 20,000Hz. C) a frequency between 40kHz and 40MHz. D) any frequency at all. Whenever molecules vibrate, human ears hear them. 44. Dolphins can hear sound waves at very high frequencies as high as 40,000 Hz. A sound wave with this high frequency would be labeled A) infrasonic. C) ultrasonic. B) audible. D) radiosonic. 45. What is the speed of sound through the vacuum of space? A) Zero. Sound cannot travel through space. B) Low, but not zero. Sound travels through space at the same speed as it travels through air, v 340m/s. C) High: sound travels through space at the same speed as it travels through steel, about v 6000m/s. D) Very high: sound travels through space at the same speed as light travels, v = m/s. 46. Compare the speed of sound through air to sound traveling through steel. A) Sound travels faster through steel because steel is an elastic material. B) Sound travels at the same speed through both, because the speed of sound is a constant. C) Sound travels faster through the air because air is less dense than steel (fewer molecules get in the way). D) No comparison can be made because the speed of sound also depends on temperature. At high temperature, steel is faster; but at low temps, air is. 47. Why does sound travel faster in warm air than cold? A) It doesn't. Sound travels faster in cold air, because cold air id denser. B) Warm air is denser than cold, so sound travels faster. C) Warm air molecules are moving faster than cold air molecules, so sound travels faster. D) Warm air is made of oxygen, and cold air is made of nitrogen. Oxygen is a faster medium than nitrogen. 48. Why is humid air a faster medium for sound than dry air? A) Because water is denser than air, and a denser medium is always a faster medium. B) Because air does not transmit sound waves at all; only the water molecules actually transmit the sound energy. C) Air molecules are heavier than water molecules. With the same amount of kinetic energy, the lighter water molecules have greater speed. D) The speed of sound is exactly the same no matter what the humidity or the temperature. The speed of sound is a constant value through all media that transmit sound. Air, water, steel it s all the same speed, about 340 m/s. 49. A depth-sounding vessel surveys the ocean bottom by sending out an ultrasonic pulse. The vessel receives the echo after t = 3 sec. If the pulse has a speed v = 1530m/s, how deep is the ocean floor? d = vt = (1530 m /s)(1.5s)=2295m A) d = 510m C) d = 1530m E) d = 3060m B) d = 1020m D) d = 2295m F) d = 4590m EXAM 02 PAGE 04

5 50. How is refraction different from reflection? A) Refraction only happens to longitudinal waves (like sound waves) and reflection only happens to transverse waves (like light waves). B) When a wave is reflected, it bounces straight back in the direction from which it came. When a wave is refracted, it bounces off the boundary in some random direction. C) A reflected wave strikes a boundary and keeps going, but it slows down. A refracted wave strikes the same boundary and keeps going, but it speeds up. D) Reflection occurs when a wave strikes a boundary that it cannot cross, so it bounces. Refraction occurs when the wave strikes a boundary, but can continue to travel through the new medium at a different speed. 51. Two transverse waves have the same amplitude, frequency, and wavelength. If they are out of phase, the resulting superposition will be A) a wave with twice the amplitude. B) a wave with twice the wavelength. C) a wave with twice the frequency. D) canceled completely; there will be no wave at all. 52. Two transverse waves have the same amplitude, frequency, and wavelength. If they interfere constructively, they are A) in phase, and reinforce each other. B) out of phase, and cancel each other. C) perpendicular and do not interact. D) parallel and cannot be seen. Please make sure that you double-check your responses before you click SUBMIT! Once you click SUBMIT, your responses are final and cannot be changed! EXAM 02 PAGE 05

Chapter 20: Mechanical Waves

Chapter 20: Mechanical Waves Section 20.1: Observations: Pulses and Wave Motion Oscillation Plus Propagation Oscillation (or vibration): Periodic motion (back-and-forth, upand-down) The motion repeats