Final Exam

Question 1

A point against which position is measured

Answer 1

Reference point

Question 2

A physical measurement that contains directional information

Answer 2

Vector quantity

Question 3

A physical measurement that does not contain directional information

Answer 3

Scalar quantity

Question 4

The time rate of change of an object’s velocity

Answer 4

Acceleration

Question 5

The motion of an object when it is falling solely under the influence of gravity

Answer 5

Free fall

Question 6

Why must one use a reference point to determine whether or not an object is in motion?

Answer 6

In order for motion to occur, an object’s position must change. In order to determine position, there must be a reference point. The reference point allows you to determine whether or not position changes.

Question 7

After a visit to your grandmother’s house, you get in your car to go home. You are in the front passenger’s seat and your mother is driving. As you back out of your grandmother’s driveway, she stands outside, waving good-bye.

a. Who is in motion relative to you?
b. Who is motionless relative to you?

Answer 7

a. Your grandmother is in motion relative to you. Even though your grandmother is standing still, her position relative to you is changing. Thus, she is in motion relative to you.
b. Your mother is motionless relative to you. Her position relative to you does not change. She is therefore motionless with respect to you.

Question 8

How many miles per hour does a car travel if it makes a 40-mile trip in 30 minutes?

Answer 8

This problem gives us distance and time and asks for speed. We know it is asking for speed because a distance unit divided by a time unit is speed or velocity. There is no direction here, so we are talking about speed. Thus, we need to use Equation (9.1). The problem wants the answer in miles per hour, however. We are given the time in minutes. Thus, we must make a conversion first:

Question 9

What is the velocity of a bicycle (in meters per second) if it travels 1 kilometer west in 4.1 minutes?

Answer 9

The problem wants velocity, which is speed and direction. To get speed, we will use Equation (9.1). Unfortunately, the problem tells us to give the answer in meters per second, but the distance is in kilometers and the time is in minutes. Thus, we need to do two conversions:

Question 10

You are looking in a scientist’s lab notebook and find the following unlabeled measurements. In each case, determine what physical quantity the scientist was measuring.

a. 12.1 meters per second
b. 31.2 feet
c. 14 millimeters per hour to the west
d. 4.5 yards per minute² north

Answer 10

a. This measurement has a distance unit divided by a time unit. That’s speed or velocity. Since no direction is given, this is speed.
b. The unit of feet by itself measures distance.
c. This measurement has a distance unit divided by a time unit. That’s speed or velocity. Since a direction is given, this is velocity.
d. This measurement has a distance unit divided by a time unit squared. That’s acceleration. The direction is necessary because acceleration is a vector quantity.

Question 11

An eagle swoops down to catch a baby rabbit. Luckily for the rabbit, he sees the eagle and runs. An all-out chase ensues with the rabbit running east at 5.4 meters per second and the eagle pursuing at 4.4 meters per second. What is the relative velocity of predator and prey?

Answer 11

As the picture shows, the eagle is behind the rabbit, but they are both traveling in the same direction. Thus, we get their relative velocity by subtracting their individual velocities:

relative velocity = 5.4 meters/second - 4.4 meters/second = 1.0 meter/second

Since the rabbit is traveling faster than the eagle, the rabbit is pulling away. Thus, the relative velocity is 1.0 meter per second away from each other.

Question 12

What is the acceleration of an object that moves with a constant velocity?

Answer 12

Since the velocity is not changing, the acceleration is zero.

Question 13

A skier reaches the bottom of a slope with a velocity of 12 meters per second north. If the skier comes to a complete stop in 3 seconds, what was her acceleration?

Answer 13

The initial velocity is 12 meters per second north, and the final velocity is 0. The time is 3 seconds. This is a straightforward application of Equation (9.2).

Question 14

A car goes from 0 to 60 miles per hour north in 5 seconds. What is the car’s acceleration?

Answer 14

This is another application of Equation (9.2), because we are given time (5 seconds), initial velocity (0) and final velocity (60 miles per hour north). We can’t use the equation yet, however, because our time units do not agree. We’ll fix that first:

Question 15

A person standing on a bridge over a river holds a rock and a ball in each hand. He throws the ball down towards the river as hard as he can and at the same time simply drops the rock. After both have left the person’s hand, does one have a greater acceleration? If so, which one?

Answer 15

Neither has greater acceleration. Both objects are falling near the surface of the earth; thus, they are each in free fall. That means they both have equal acceleration. The ball was given moreinitial velocity, so it will travel faster. The acceleration on both is the same, however.

Question 16

Why does a dropped feather hit the ground later than a rock dropped at the same time?

Answer 16

The feather is more affected by air resistance than the rock. This is the same situation as Experiment 9.2.

Question 17

A physics student climbs a tree. To measure how high she has climbed, she drops a rock and times its fall. It takes 1.3 seconds for the rock to hit the ground. How many feet has she climbed?

Answer 17

The rock is in free fall, so we can use Equation (9.3). Since the problem wants the answer in feet, we need to use 32 feet per second² as the acceleration.

Question 18

The tendency of an object to resist changes in its velocity

Answer 18

Inertia

Question 19

A force that opposes motion, resulting from the contact of two surfaces

Answer 19

Friction

Question 20

Friction that opposes motion once the motion has already started

Answer 20

Kinetic friction

Question 21

Friction that opposes the initiation of motion

Answer 21

Static friction

Question 22

State Newton’s three laws of motion.

Answer 22

Newton’s First Law – An object in motion (or at rest) will tend to stay in motion (or at rest) until it is acted upon by an outside force.

Newton’s Second Law – When an object is acted on by one or more outside forces, the total force is equal to the mass of the object times the resulting acceleration

Newton’s Third Law – For every action, there is an equal and opposite reaction.

Question 23

A pilot is flying a mission to drop bombs on an enemy airfield. The plane is flying high and fast to the north, and the city is due north. Should the pilot drop the bombs before the plane is over the airfield, when the plane is over the airfield, or after the plane has passed the airfield?

Answer 23

The pilot must drop the bombs before the plane reaches the airfield. The bombs will have a velocity equal to that of the plane when they are dropped. Thus, they will continue to fly north as they fall. In order to hit the airfield, then, they must be dropped south of it.

Question 24

A cruel boy has placed a mouse on the outer edge of a disk. He slowly starts to spin the disk, accelerating it faster and faster until the disk and mouse are both spinning around at an alarming rate. What will happen to the mouse if the boy suddenly stops the disk without touching the mouse: will the mouse continue to spin like it was before; will the mouse stop with the disk; or will the mouse start moving straight, skidding off the disk?

Answer 24

The mouse will start moving straight, skidding off of the disk. This is like Experiment 10.2. When the disk stops, the mouse has a velocity pointed in a certain direction. Without sufficient time, the frictional force will not be able to keep the mouse on the disk. This will cause the mouse to start traveling in a straight line, in the direction it was moving right before the disk stopped.

Question 25

An ice cube (mass = 1.0 kg) slides down an inclined serving tray with an acceleration of 4.0 meters per second². Ignoring friction, how much force is pulling the ice cube down the serving tray?

Answer 25

Since we are ignoring friction, this is an easy problem:

Question 26

A baseball player (mass = 75 kilograms) is running north towards a base. In order to avoid being tagged by the ball, the baseball player slides into the base. If his acceleration in the slide is 5.0 meters per second² south, what is the kinetic frictional force between the baseball player and the ground?

Answer 26

The baseball player is slowing, because his velocity is north but the acceleration is directed south. Friction slows things down. This is the only force in the problem, since nothing else is pulling or pushing on the player. Thus, the force that results from the acceleration will be the frictional force.

Question 27

A man pushes a heavy cart. If the man exerts a force of 200 Newtons on the cart to keep it moving at a constant velocity, what is the frictional force between the cart and the ground? Is this kinetic friction or static friction?

Answer 27

If the cart is moving with a constant velocity, that means the acceleration (and thus the total force) equals zero. Thus, the man must be pushing with just enough force to counteract friction. Thus, the frictional force is _200 Newtons against the motion of the cart. This is kinetic friction, because the cart is moving_.

Question 28

You are looking through a physicist’s laboratory notebook and notice two numbers for the friction between a block of wood and a laboratory bench. The numbers are 8 Newtons and 11 Newtons. Which refers to static friction and which refers to kinetic friction?

Answer 28

Since static friction is generally greater than kinetic friction, _11 Newtons refers to static friction, and 8 Newtons refers to kinetic friction_.

Question 29

A woman pushes a box (mass = 30 kilograms). The static friction between the box and the ground is 20 Newtons, while the kinetic friction is 7 Newtons. How much force must the woman exert to get the box moving? With what force must she push the box in order to get it to accelerate at 1.0 meters per second² to the west?

Answer 29

If the static frictional force is 20 Newtons, the woman must overcome it to get the box moving. _To get the box moving, then, a force greater than 20 Newtons must be used_. Once the box is moving, the acceleration is 1.0 meters per second2, so the total force is:

Question 30

When baseball players hit the ball hard enough, their bats can sometimes break. What is exerting a force on the bat, causing it to break?

Answer 30

_The ball exerts a force on the bat_. This is the equal and opposite force demanded by Newton’s Third Law.

Question 31

What theory says that gravity is caused by the exchange of particles between objects with mass?

Answer 31

The Graviton Theory

Question 32

A child is twirling a toy airplane on a string at a constant speed: Which arrow represents the force the plane is experiencing?

Answer 32

Arrow A

Question 33

The weakest of the fundamental forces is gravity.

Answer 33

True

Question 34

The gravitational force between two objects (mass1 = 5 kg, mass₂ = 2 kg) is measured when the objects are 10 centimeters apart. If the 5 kg mass is replaced with a 20 kg mass and the 2 kg mass is replaced with a 12 kg mass, how does the new gravitational attraction compare to the first one that was measured?

Answer 34

The new gravitational force is 24 times larger than the old one.

Question 35

Use the following diagram to answer the question. Which of the orbits is more likely that of a comet?

Answer 35

orbit c

Question 36

The gravitational force between two objects (mass1 = 10 kg, mass₂ = 6 kg) is measured when the objects are 12 centimeters apart. If the distance between them is increased to 36 centimeters, how does the new gravitational attraction compare to the first one that was measured?

Answer 36

The new gravitational force is 9 times smaller than the old one.

Question 37

Suppose a scientist determines that there are only two fundamental forces in nature: the electroweak force and the strong force. Which of the two current theories of gravity does this mean is true?

Answer 37

The Graviton Theory would be true in this case.

Question 38

A child is twirling a toy airplane on a string at a constant speed: Which arrow represents the velocity of the plane?

Answer 38

Arrow C

Question 39

A child is twirling a toy airplane on a string at a constant speed: What kind of force is the plane experiencing (as shown by one of the arrows)?

Answer 39

Centripetal force

Question 40

Two moons orbit different planets, but they orbit their planets at the same distance. If the first one takes 3 months to make an orbit and the second takes 1 year, which is being subjected to the greatest gravitational attraction?

Answer 40

The first moon experiences the greatest gravitational force.

Question 41

Jupiter is the planet in the solar system that receives the least amount of insolation.

Answer 41

False

Question 42

A student drops a ball, and it begins to fall due to the force of gravity that the earth exerts on it. What is the equal and opposite force demanded by Newton’s Third Law of Motion?

Answer 42

The equal and opposite force is the earth's gravity, or if you were talking about the ball, it would be the ball's mass.

Question 43

The Kuiper belt is a source of long-term comets.

Answer 43

False

Question 44

What part or parts of a comet come and go during a comet’s orbit?

Answer 44

The coma and tail come and go, depending on the proximity to the sun.

Question 45

The outer planets are Mars, Jupiter, Saturn, Neptune, Pluto.

Answer 45

False

Question 46

The force between the south pole of one magnet and the south pole of another magnet is measured. The distance between those magnets is suddenly doubled. How will the new force compare with the old one?

Answer 46

The new force decreases by a factor of four.

Question 47

The force between the south pole of one magnet and the south pole of another magnet is measured. The distance between those magnets is suddenly doubled.

Answer 47

Repulsive

Question 48

You cut a magnet in half - right between the north and south poles. How many north poles and south poles do you now have?

Answer 48

You will have two north poles and two south poles.

Question 49

A physicist charges an object with a positively-charged rod. If the object develops a negative charge, how did the physicist charge the object?

Answer 49

The object developed a charge opposite of the rod. Thus, the object was charged by induction.

Question 50

A measure of how much a metal impedes the flow of electrons.

Answer 50

Resistance

Question 51

Small “packages” of light that act just like small particles.

Answer 51

Photons

Question 52

A circuit that does not have a complete connection between the two sides of the battery. As a result, current does not flow.

Answer 52

Open circuit

Question 53

Charging an object by forcing some of the charges to leave the object.

Answer 53

Charging by induction

Question 54

Charging an object by allowing it to come into contact with an object which already has an electrical charge.

Answer 54

Charging by conduction

Question 55

Current that flows from the positive side of the battery to the negative side. This is the way current is drawn in circuit diagrams, even though it is wrong.

Answer 55

Conventional current

Question 56

The amount of charge that travels through an electrical circuit each second.

Answer 56

Electrical current

Question 57

The atoms in an object are not aligned. Is the object a magnet? Why or why not?

Answer 57

No. A magnet must have their atoms aligned in order for it to be considered a magnet.

Question 58

In most chandeliers today, when one light bulb goes out, the rest stay lit. Are the light bulbs wired in series or in parallel?

Answer 58

The light bulbs are wired in parallel.

Question 59

Will the objects shown bellow attract or repel each other?

Answer 59

The two objects have opposite charges, so they will attract each other.

Question 60

Look at the circuit diagram below: Which arrow represents the conventional current flow?

Answer 60

The dashed line and arrows.

Question 61

You are blindfolded and handed two extension cords. Both have the same current running through them. If the cord in your left hand is warmer than the one in your right hand, which cord is thicker?

Answer 61

The cord in your right hand.

Question 62

If a circuit has a low voltage, is there any way to get a lot of energy from it? If so, how?

Answer 62

A low voltage means that each electron will have only a little bit of energy. You can still get a lot of energy out of the circuit, however, as long as you put a lot of current through it.

Question 63

Look at the circuit diagram below: Which arrow represents the flow of electrons?

Answer 63

The solid line and arrows.

Question 64

The center of an atom, containing the protons and neutrons

Answer 64

Nucleus

Question 65

The number of protons in an atom

Answer 65

Atomic number

Question 66

The sum of the numbers of neutrons and protons in the nucleus of an atom

Answer 66

Mass number

Question 67

Atoms with the same number of protons but different numbers of neutrons

Answer 67

Isotopes

Question 68

A collection of atoms that all have the same number of protons

Answer 68

Element

Question 69

An atom with a nucleus that is not stable

Answer 69

Radioactive isotope

Question 70

Which is larger, an electron or a proton? Which is negatively charged?

Answer 70

A _proton_ is larger than an electron. An _electron_ is negatively charged.

Question 71

What causes the nuclear force, and why can this force act only over very short distances?

Answer 71

The nuclear force is caused by _the exchange of pions_. It is a short-range force because _pions can only exist for a short time_.

Question 72

List the number of protons, neutrons, and electrons in the following atoms: a. ⁴⁸Ca b. ¹²⁴Sn c. ¹⁰⁹Ag

Answer 72

a. Since the chemical symbol is Ca, we can use the chart to learn that the atom has _20 protons_. This tells us there are also _20 electrons_. The mass number is the sum of protons and neutrons in the nucleus. Thus, there are _28 neutrons_. b. Since the chemical symbol is Sn, we can use the chart to learn that the atom has _50 protons_. This tells us there are also _50 electrons_. The mass number is the sum or protons and neutrons in the nucleus. Thus, there are _74 neutrons_. c. Since the chemical symbol is Ag, we can use the chart to learn that the atom has _47 protons_. This tells us there are also _47 electrons_. The mass number is the sum of protons and neutrons in the nucleus. Thus, there are _62 neutrons_.

Question 73

Draw an illustration of what the Bohr model says a ²³Na atom looks like.

Answer 73

All atoms symbolized with “Na” have 11 protons according to the chart. This also means there are 11 electrons. Two of them can go into the first Bohr orbit, and 8 can go in the second Bohr orbit. We will have to put the remaining one in the third Bohr orbit. The mass number indicates that there are 12 neutrons:

Question 74

Which of the following atoms are isotopes? ¹⁴⁴Ce, ¹⁴⁴Nd, ¹⁴⁴Sm, ¹⁴⁵Nd

Answer 74

Isotopes have the same number of protons but different numbers of neutrons. Since chemical symbols tell us the number of protons, we are looking for atoms with the same chemical symbol but different mass numbers. Thus, ¹⁴⁴_Nd and ¹⁴⁵Nd are isotopes_.

Question 75

A radioactive isotope has a half-life of 3 hours. If a scientist has 30 grams of the isotope, how much is left after 15 hours?

Answer 75

In the first three hours, the 30 gram sample will be reduced to 15 grams. In the next three hours, it will be reduced to 7.5 grams. In the next 3 hours, it will be reduced to 3.75 grams. In the next three hours, it will be reduced to 1.875 grams. In the next 3 hours, it will be reduced to _0.9375 grams_.

Question 76

What is the daughter product in the beta decay of ¹⁴⁴Ce?

Answer 76

¹⁴⁴Ce has 58 protons according to the chart. This means there must be 86 neutrons. In beta decay, a neutron turns into a proton. This will result in an atom with 59 protons and 85 neutrons, or _¹⁴⁴Pr_.

Question 77

What is the daughter product in the alpha decay of ²²⁰Rn?

Answer 77

²²⁰Rn has 86 protons according to the chart. This means there must 134 neutrons. In alpha decay, the nucleus loses 2 protons and 2 neutrons. This will result in an atom with 84 protons and 132 neutrons, or _²¹⁶Po_.

Question 78

What is the daughter product in the gamma decay of ²³⁹U?

Answer 78

In gamma decay, the number of protons and neutrons is unaffected by the decay. Thus, the daughter product is the same as the original _²³⁹U_.

Question 79

If a piece of paper is placed between a radioactive isotope and a person, which kind of radioactive particle will the person be protected from?

Answer 79

The person would only be protected from _alpha particles_.

Question 80

Which waves have the longest wavelength?

Answer 80

Infrasonic waves

Question 81

An amplifier at a concert takes a 30 decibel sound and turns it into an 80 decibel sound. Is the amplified sound loud enough to damage a person’s eardrum?

Answer 81

No, 80 decibels is within a normal person’s hearing threshold.

Question 82

A jet travels through 10˚C air at Mach 3. What is its speed in meters per second? (Show your work.)

Answer 82

(331. 5 + 0.6 • 10) m/sec 337. 5 m/sec • 3 _1012.5 m/sec_

Question 83

During a thunderstorm, the temperature is 10˚C. If you see a lightning strike and then hear the thunder 2 seconds later, how far away did the lightning strike?

Answer 83

675 m

Question 84

What is the speed of sound in air that has a temperature of 25˚C?

Answer 84

346.5 m/sec

Question 85

A man and woman are singing a duet. The man sings the low notes and the woman sings the high notes. The woman, since she is singing the melody, is louder than the man. How do the wavelengths of the man’s sound waves compare to those of the woman?

Answer 85

The man’s sound waves have longer wavelengths than the woman’s.

Question 86

A sound wave traveling through 17˚C air has a wavelength of 2 meters. What is the frequency of the sound wave? (Show your work.)

Answer 86

(331. 5 + 0.6 • 17) m/sec 341. 7 m/sec/ 2m _170.85 1/sec_

Question 87

An amplifier at a concert takes a 30 decibel sound and turns it into an 80 decibel sound. How many times larger is the intensity of the sound waves coming out of the amplifier as compared to the intensity of the sound waves going into the amplifier?

Answer 87

The sound wave intensity is 100,000 times larger.

Question 88

A ship blows its horn. Some of the sound waves travel through the air and then hit the water. Will the sound waves travel faster in the water or in the air?

Answer 88

The sound waves will travel faster in the water.

Question 89

A popular science fiction movie was advertised with the slogan, “In space, no one can hear you scream.” Is this a true statement? Why or why not?

Answer 89

Yes. Since there is no air in space, our voices, or any sound, cannot be heard because the sound waves are blocked.

Question 90

Do sound waves oscillate parallel to or perpendicular to the direction in which the wave travels?

Answer 90

Parallel

Question 91

You are driving in a city that has a siren which sounds for 30 seconds every day at noon. You stop at a stoplight and then hear the sound of the siren. The stoplight then turns green, and you start driving. As you speed up, you notice that the pitch of the siren keeps getting higher. Are you driving towards or away from the siren? (Assume that the true pitch of the siren stays constant.)

Answer 91

You are driving towards the siren.

Question 92

The highness or lowness of a sound.

Answer 92

Pitch

Question 93

The lowest point in a wave.

Answer 93

Trough

Question 94

A wave whose propagation is parallel to its oscillation.

Answer 94

Longitudinal wave

Question 95

The highest point in a wave.

Answer 95

Crest

Question 96

Any speed that is faster than the speed of sound in the substance of interest.

Answer 96

Supersonic speed

Question 97

The sound produced as a result of aircraft traveling at or above Mach 1.

Answer 97

Sonic boom

Question 98

A wave whose propagation is perpendicular to its oscillation.

Answer 98

Transverse wave

Question 99

A man and woman are singing a duet. The man sings the low notes and the woman sings the high notes. The woman, since she is singing the melody, is louder than the man. How do the speed of the sound waves compare?

Answer 99

The man’s sound waves have the same speed as the woman’s.

Question 100

A man and woman are singing a duet. The man sings the low notes and the woman sings the high notes. The woman, since she is singing the melody, is louder than the man. How do the amplitudes of the waves compare?

Answer 100

The man’s sound waves have smaller amplitude than the woman’s.

Question 101

A man and woman are singing a duet. The man sings the low notes and the woman sings the high notes. The woman, since she is singing the melody, is louder than the man. How do the frequency of the man’s sound waves compare to those of the woman?

Answer 101

The man’s sound waves have lower frequencies than the woman’s.

Question 102

A recorder is a woodwind instrument in which the player blows into a tube, setting up a wave in the tube. A musician has 2 recorders. The first one is rather short, and the second one is significantly longer. Which recorder is capable of playing notes with the lowest pitch?

Answer 102

The long recorder.

Question 103

What does the eye do to change its focus?

Answer 103

To change its focus, the eye changes the shape of the lens.

Question 104

You are on a diving board looking down into a pool. You see a quarter at the bottom of the pool, about three feet in front of you. Why is the quarter really not 3 feet in front of you? Where is it?

Answer 104

Water refracts light, making objects appear at a different place. The quarter is closer to you.

Question 105

The angle of reflection equals the angle of incidence.

Answer 105

The Law of Reflection

Question 106

The subtractive primary colors.

Answer 106

Magenta, yellow, and cyan

Question 107

The light which we see with our eyes.

Answer 107

Visible spectrum

Question 108

A representation of all the light in Creation.

Answer 108

Electromagnetic spectrum

Question 109

A transverse wave composed of an oscillating electrical field and a magnetic field that oscillates perpendicular to the electrical field.

Answer 109

Electromagnetic wave

Question 110

The additive primary colors.

Answer 110

Red, green, and blue

Question 111

Which has the highest frequency?

Answer 111

blue light

Question 112

For the next few questions, remember that blue + green = cyan, red + blue = magenta, and red + green = yellow. If cyan and magenta ink is mixed, what color ink will you get?

Answer 112

ou will get blue ink.

Question 113

Which has longest wavelength?

Answer 113

radio waves

Question 114

The speed of light in glass is 185,000,000 m/sec. If a particle is traveling through air at 200,000,000 m/sec, what has to happen to the particle’s speed if it enters the glass?

Answer 114

It will slow down.

Question 115

Describe light according to the currently accepted theory. Be very detailed.

Answer 115

According to the accepted theory, light is both a particle and a wave. It looks like it is made up of particles, but it acts like a wave. There are individual packets of light in a wave-like sequence.

Question 116

You want to concentrate light coming from a weak light source by focusing it all on a single point. Would you use a converging or diverging lens to do this?

Answer 116

A converging lens

Question 117

Which picture shows what happens to the light ray when it hits the right side of the aquarium?

Answer 117

Picture d

Question 118

For the next few questions, remember that blue + green = cyan, red + blue = magenta, and red + green = yellow. If a computer monitor makes a green dot and then puts a blue dot in the same place, what color will you see?

Answer 118

You will see a cyan dot.

Question 119

For the next few questions, remember that blue + green = cyan, red + blue = magenta, and red + green = yellow. If you shine red light on a yellow shirt, what color will the shirt appear?

Answer 119

It will appear red.

Question 120

The process by which two or more small nuclei fuse to make a bigger nucleus

Answer 120

Nuclear fusion

Question 121

The process by which a large nucleus is split into smaller nuclei

Answer 121

Nuclear fission

Question 122

The amount of isotope necessary to sustain a chain reaction

Answer 122

Critical mass

Question 123

The brightness of a star, corrected for distance, on a scale of -8 to +19. The *smaller* the number, the *brighter* the star.

Answer 123

Absolute magnitude

Question 124

The brightness of a star as seen in the night sky. The *smaller* the number, the *brighter* the star.

Answer 124

Apparent magnitude

Question 125

The distance light could travel along a straight line in one year

Answer 125

Light year

Question 126

A large ensemble of stars, all interacting through the gravitational force and orbiting around a common center

Answer 126

Galaxy

Question 127

What nuclear process occurs in the sun’s core?

Answer 127

_Nuclear fusion_ occurs in the sun’s core.

Question 128

A ⁴He nucleus and a ⁷Li nucleus collide and form a ¹⁰B nucleus and a neutron. Is this nuclear fusion or nuclear fission?

Answer 128

_This is nuclear fusion_, since two small nuclei fused to make a bigger one.

Question 129

A scientist studies a process in which a neutron strikes a ²¹⁶Pu nucleus to make a ¹⁰⁴Cd nucleus, a ¹¹⁰Pd nucleus, and three neutrons. If the scientist measures the mass of the ²¹⁶Pu and the original neutron and then subtracts the mass of the ¹⁰⁴Cd nucleus, the mass of the ¹¹⁰Pd nucleus, and the mass of the three neutrons, will the scientist get a positive number, a negative number, or zero?

Answer 129

He would get a _positive number_. In nuclear fission and fusion, mass is converted into energy. Thus, the mass of the materials produced will be less than the mass of the starting materials.

Question 130

Is it possible for a nuclear power plant to experience a nuclear explosion? Why or why not?

Answer 130

_It is not possible, because a power plant does not have significantly more than the critical mass of the large nucleus_.

Question 131

Using the H-R diagram below, classify the following stars: a. Magnitude 5, Spectral Letter G b. Magnitude 2, Spectral Letter K c. Magnitude 11, Spectral Letter B d. Magnitude -6, Spectral Letter A

Answer 131

Using the magnitudes and spectral letters given, we have: This tells us the classifications are: a. _Main sequence_ b. _Red giant_ c. _White dwarf_ d. _Supergiant_

Question 132

Which is the brightest of the stars in problem #6?

Answer 132

The brightest star is the one with the lowest magnitude. Thus, _(d)_ is the brightest star.

Question 133

Which is the hottest of the stars in problem #6?

Answer 133

The hottest star is the one that is the farthest to the left on the H-R diagram, because temperature increases the farther left you travel on the H-R diagram. Thus, _(c)_ is the hottest star.

Question 134

What are the two main types of variable stars?

Answer 134

The two main types of variable stars are _novas_ and _pulsating variables_.

Question 135

What are Cepheid variables, and why are they important in astronomy?

Answer 135

_Cepheid variables are variable stars whose magnitude and period have a direct relationship. They are important in astronomy because that relationship can be used to measure long distances in the universe_.

Question 136

What is the name of the galaxy to which earth’s solar system belongs? What type of galaxy is it?

Answer 136

Earth’s solar system belongs to the _Milky Way_ galaxy, which is a _spiral galaxy_.

Question 137

What is the red shift?

Answer 137

_The red shift is the phenomenon in which light that comes to the earth from other galaxies ends up having longer wavelengths than it should_. Most astronomers interpret that as a Doppler shift resulting from the expansion of the universe.