Question #3
what were the two most important sources of the heat that melted the entire early earth, allowing materials of different density to differentiate?
heat released by collision processes during accretion, and heat from decay of radioactive elements
heat from fires on the early earth, and heat from the sun
heat from decay of radioactive elements, and heat from the sun
heat from the sun, and heat released by volcanic eruptions
heat from fires on the early earth, and heat released by volcanic eruptions
question #4
which of the following statements is true regarding spacecraft trajectories near planets at orbital speeds above the escape velocity?
the spacecraft will be captured by the planet.
the spacecraft will proceed in a straight line and not be deflected.
the spacecraft will always have the same overall speed before the encounter as after it.
this is impossible; spacecraft must always stay in orbit and can never exceed escape velocity.
the spacecraft can either gain or lose orbital speed during the encounter depending on the exact orbit.