5) Astrophysics

Question 1

What is the universe?

Answer 1

• a large collection of billions of galaxies

Question 2

What is a galaxy?

Answer 2

• a large collection of billions of stars

Question 3

What is the name of our solar system?

Answer 3

• milky way

Question 4

What does the gravitational field strength of a planet depend on?

Answer 4

• radius of planet

- density of planet

Question 5

What is the relationship between mass and gravitational force?

Answer 5

gravitational force is directly proportional to the mass

Question 6

What is the relationship between gravitational force and distance?

Answer 6

gravitational force is inversely proportional to the distance

Question 7

As the distance increases, the gravitational force ___________

Answer 7

• decreases

Question 8

As the mass increases, the gravitational force ___________

Answer 8

• increases

Question 9

What is the equation to find orbital speed (v)?

Answer 9

v = 2πr/T
v = orbital speed (km/s)
r = orbital radius (km)
T = time period (seconds)

Question 10

Why does gravity cause things to orbit things (in general)

Answer 10

• gravity pulls things to the ground

- gravity acts on all stars, planets, moons

Question 11

When is GPE strongest?

Answer 11

• furthest away

Question 12

What is a comet?

Answer 12

• ball of dust and ice that travels through the solar system

Question 13

What type of orbits do comets have?

Answer 13

• elongated elliptical orbits

Question 14

Why do comets have 2 tails?

Answer 14

• gas tail - points directly away from the Sun due to ‘solar winds’ (electrically charged particles streaming out of the Sun) that push it back
• dust tail - lags behind the gas tail

Question 15

Describe the orbit of a comet referring to its GPE and KE:

Answer 15

• KE is fastest when close to the Sun
• GPE is lowest when close to the Sun
• KE of comet decreases as gravitational pull decreases when comet is moving away from Sun
• GPE increases as comet moves away from Sun
• KE lowest when furthest from Sun
• GPE highest when furthest from Sun
• GPE decreases as comet moves towards Sun
• KE increases as comet moves towards Sun as gravitational pull increases

Question 16

How are stars classified?

Answer 16

• according to their colour

Question 17

What is the order of star classification from highest temperature to lowest temperature? What is each of these classes temperature? What is each of these classes colour?

Answer 17

O - more than 33,000 K - blue
B - 10,000 - 33,000 K - blue white
A - 7,500 - 10,000 K - white
F - 6,000 - 7,500 K - yellow white
G - 5,200 - 6,000 K - yellow
K - 3,700 - 5,200 K - orange
M - 2,000 - 3,700 K - red

Question 18

What is the life cycle of a star that has a similar mass to the Sun?

Answer 18

• stellar nebula
• main sequence star
• red giant
• white dwarf
• black dwarf

Question 19

What is the life cycle of a star that has a greater mass than the Sun?

Answer 19

• stellar nebula
• main sequence
• red super giant
• supernova
• neutron star
• black hole

Question 20

What is a stellar nebula?

Answer 20

• cloud of cold hydrogen gas and dust which is collapsing due to the pull of gravity

Question 21

What is main sequence star?

Answer 21

• the star releases energy from the fusion of hydrogen to form helium
• the forces are balanced

Question 22

How does a main sequence star become a red giant?

Answer 22

• due to hydrogen shortage, the main sequence star becomes unstable
• the outward forces decrease and the star begins to collapse
• this brings additional hydrogen into a zone where the temperature and pressure are sufficient to cause fusion
• the outer layers expand greatly and the star enters the red giant phase

Question 23

How does a red giant become a white dwarf?

Answer 23

• helium starts to fuse to make heavier elements such as carbon and oxygen
• eventually the star is no longer able to fuse helium and its core cools down
• the star collapses into a white dwarf

Question 24

How does a white dwarf become a black dwarf?

Answer 24

• the white dwarf starts to cool down and it will eventually become a dark cold star

Question 25

What happens in a red super giant?

Answer 25

• temperature in the core is so high that helium nuclei fuse to form heavier elements
• elements as heavy as iron are produced by fusion

Question 26

How does a red super giant become a supernova?

Answer 26

• red super giant runs out of nuclear fuel
• forces of gravity overcome the outwards pressure from the center of the star
• rapid collapse heats the inside of the star to such high temperatures that there is a nuclear reaction
• the star explodes like a cosmic nuclear bomb
• elements heavier than iron are made

Question 27

How does a red super giant become a neutron star or a black hole?

Answer 27

• red super giant runs out of nuclear fuel
• forces of gravity overcome the outwards pressure from the center of the star
• star collapses rapidly
• great gravitational forces cause the center to collapse into a highly condensed form of matter
• might be left as a neutron star made only of neutrons
• collapse may be so complete that the star disappears and has become a black hole
• black hole is so dense that nothing, including light, can escape from it