Why do flat disks form around young stars?
A) They don't; the stars form from the disks.
B) Centrifugal force pushes gas outward from the spinning gas cloud.
C) Intense winds from nearby massive stars flatten the gas cloud.
D) Collisions between rotating gas particles flatten the gas cloud along the axis of rotation.
Question 2Which of the following describes erosion?
A) the excavation of bowl-shaped depressions by asteroids or comets striking a planet's surface
B) the eruption of molten rock from a planet's interior to its surface
C) the disruption of a planet's surface by internal stresses
D) the wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather
Question 3What is the source of luminosity for protostars that have not yet become hot enough for fusion in their cores?
A) light absorbed from nearby stars B) energy released by infalling matter
C) fusion in their low-density outer layers D) fission from concentrated radioactive elements
Question 4The force due to gravity between two objects can be described using the equation Fg = G M1 M2 / d2. According to this equation, if the mass of the second object were greater, what happens to the gravitational force between them?
A) The force increases.
B) The force decreases.
C) The force drops instantly to zero.
D) The gravitational force is not affected by the mass of the second object.
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