Midterm 2

Question 1

If you drop a rock from a great height, about how fast will it be falling after 5 seconds, neglecting air
resistance?

Answer 1

50 m/s

Question 2

If your mass is 60 kg on Earth, what would your mass be on the Moon?

Answer 2

60 kg

Question 3

If an object’s velocity is doubled, its momentum is

Answer 3

doubled.

Question 4

Newton’s second law of motion tells us that the net force applied to an object equals its

Answer 4

mass times acceleration.

Question 5

What quantities does angular momentum depend upon?

Answer 5

mass, velocity, and radius

Question 6

What does temperature measure?

Answer 6

the average kinetic energy of particles in a substance

Question 7

Suppose you heat up an oven and boil a pot of water. Why would you be burned by sticking your hand briefly in the pot but not by sticking your hand briefly in the oven?

Answer 7

The water has a higher heat content than the oven.

Question 8

The amount of gravitational potential energy released as an object falls depends on

Answer 8

its mass and the distance it falls.

Question 9

Which of the following statements correctly describes the law of conservation of energy?
A) Energy can change between many different forms, such as potential, kinetic, and thermal, but it is ultimately destroyed.
B) An object always has the same amount of energy.
C) The fact that you can fuse hydrogen into helium to produce energy means that helium can be turned into hydrogen to
produce energy.
D) It is not really possible for an object to gain or lose potential energy, because energy cannot be destroyed.
E) The total quantity of energy in the universe never changes.

Answer 9

E) The total quantity of energy in the universe never changes.

Question 10

According to the universal law of gravitation, if you triple the distance between two objects, then the gravitational force between them will

Answer 10

decrease by a factor of 9.

Question 11

The allowed shapes for orbits under the force of gravity are

Answer 11

ellipses, parabolas, and hyperbolas.

Question 12

The mass of Jupiter can be calculated by

Answer 12

measuring the orbital period and distance of one of Jupiter’s moons.

Question 13

Imagine we’ve discovered a planet orbiting another star at 1 AU every 6 months. The planet has a moon that orbits the planet at the same distance as our Moon, but it takes 2 months. What can we infer about this planet?

Answer 13

It is less massive than Earth.

Question 14

Changing the orbit of a spacecraft by firing thrusters is an example of

Answer 14

Newton’s third law of motion.

Question 15

Considering Einstein’s famous equation, E = mc2, which of the following statements is true?

Answer 15

A small amount of mass can be turned into a large amount of energy.

Question 16

The center of mass of a binary star system is

Answer 16

the point at which the two objects would balance if they were somehow connected.

Question 17

If you have a 100-watt light bulb, how much energy does it use each minute?

Answer 17

6,000 joules

Question 18

The frequency of a wave is
A) measured in cycles per second.
B) the number of peaks passing by any point each second.
C) equal to the speed of the wave divided by the wavelength of the wave.
D) measured in hertz (Hz).
E) all of the above

Answer 18

E) all of the above

Question 19

How are wavelength, frequency, and energy related for photons of light?

Answer 19

Longer wavelength means lower frequency and lower energy

Question 20

From lowest energy to highest energy, which of the following correctly orders the different categories of electromagnetic radiation?

Answer 20

radio, infrared, visible light, ultraviolet, X rays, gamma rays

Question 21

We can see each other in the classroom right now because we

Answer 21

reflect visible light.

Question 22

Consider an atom of gold in which the nucleus contains 79 protons and 118 neutrons. If it is doubly ionized,
what is the charge of the gold ion and how many electrons remain in the ion?

Answer 22

The gold ion has a charge of +2 and 77 electrons.

Question 23

At extremely high temperatures (e.g., millions of degrees), which of the following best describes the phase of
matter?

Answer 23

a plasma consisting of positively charged ions and free electrons

Question 24

Grass (that is healthy) looks green because

Answer 24

it reflects green light and absorbs other colors.

Question 25

An atom of the element iron has an atomic number of 26 and an atomic weight of 56. If it is neutral, how many protons, neutrons, and electrons does it have?

Answer 25

26 protons, 30 neutrons, 26 electrons

Question 26

Dissociation is the process in which

Answer 26

the bonds between atoms in a molecule are broken.

Question 27

When an atom absorbs a photon containing energy, any of the following can happen except which?

Answer 27

An electron moves from an upper energy level to a lower one.

Question 28

If you heat a gas so that collisions are continually bumping electrons to higher energy levels, when the
electrons fall back to lower energy levels the gas produces

Answer 28

an emission line spectrum

Question 29

Which of the following statements about thermal radiation is always true?
A) A hot object emits more total radiation than a cool object.
B) A hot object emits less total radiation than a cool object.
C) A hot object emits more radio waves than a cool object.
D) A hot object emits more X rays than a cool object.
E) A hot object emits more total radiation per unit surface area than a cool object.

Answer 29

E) A hot object emits more total radiation per unit surface area than a cool object.

Question 30

From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a
wavelength of 486.1 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing
at a wavelength of 485.9 nm. What can we conclude?

Answer 30

The star is moving toward us.

Question 31

If two objects are the same size but one object is 3 times hotter than the other object, the hotter object emits

Answer 31

81 times more energy.

Question 32

We can learn a lot about the properties of a star by studying its spectrum. All of the following statements are
true except one. Which one?

Answer 32

The total amount of light in the spectrum tells us the star’s radius.

Question 33

If we observe one edge of a planet to be redshifted and the opposite edge to be blueshifted, what can we
conclude about the planet?

Answer 33

The planet is rotating.

Question 34

Suppose you see two stars a blue star and a red star. Which of the following can you conclude about the two
stars? Assume that no Doppler shifts are involved. (Hint Think about the laws of thermal radiation.)

Answer 34

The blue star has a hotter surface temperature than the red star.

Question 35

Suppose the angular separation of two stars is smaller than the angular resolution of your eyes. How will the
stars appear to your eyes?

Answer 35

The two stars will look like a single point of light.

Question 36

What causes stars to twinkle?

Answer 36

bending of light rays by turbulent layers in the atmosphere

Question 37

Which of the following is a principal advantage of CCDs over photographic film?
A) Images recorded with CCDs never require any image processing, while images recorded by film often do.
B) CCDs can be attached to modern telescopes more easily than cameras.
C) CCDs can record the colors of astronomical objects accurately, while film cannot.
D) CCDs capture a much higher percentage of the incoming photons than does film.
E) CCDs allow long exposures (e.g., minutes or hours), and film does not.

Answer 37

CCDs capture a much higher percentage of the incoming photons than does film.

Question 38

Which of the following statements best describes the two principal advantages of telescopes over eyes?
A) Telescopes can see farther without image distortion and can record more accurate colors.
B) Telescopes have much more magnification and better angular resolution.
C) Telescopes can collect far more light with far better angular resolution.
D) Telescopes collect more light and are unaffected by twinkling.
E) Telescopes can collect far more light with far greater magnification.

Answer 38

Telescopes can collect far more light with far better angular resolution.

Question 39

Which of the following could not be measured by an observation that uses only imaging?
A) the number of bright stars in a nearby star cluster
B) the color of a planet
C) the brightness of a star in our sky
D) the rate at which a variable star brightens and dims
E) the general shape of an interstellar cloud of gas

Answer 39

D) the rate at which a variable star brightens and dims

Question 40

What is meant by spectral resolution?

Answer 40

It is a measure of how close two spectral lines can be distinguished.

Question 41

What do astronomers mean by light pollution?

Answer 41

Light pollution refers to light used for human activities that brightens the sky and hinders astronomical observations.

Question 42

Which of the following statements about light focusing is not true?
A) Light can be focused with a lens or a mirror.
B) The focal plane of a reflecting telescope is always located within a few inches of the primary mirror.
C) Film should be placed at the focal plane in a camera.
D) If you try to look at an image that is not formed at the focal plane, it will be blurry.
E) In a healthy eye, light is focused on the retina.

Answer 42

B) The focal plane of a reflecting telescope is always located within a few inches of the primary mirror.