Newton concluded that a force from the Earth had to act on the moon because
a. a force is needed to keep the moon in motion in its orbit.
b. a force is needed to pull the moon outward.
c. a force is needed to accelerate the moon toward Earth away from straight-line motion.
d. the moon moved at a constant velocity in a straight line.
e. all of the above
Question 2The extinction of starlight due to the interstellar medium I. is the greatest in the ultraviolet. II. is the greatest in the infrared. III. is caused by ionized hydrogen. IV. is caused by dust particles.
a. I & III
b. II & III
c. I & IV
d. II & IV
e. only IV
Question 3The force of gravity from one object extends to infinity never going to zero.When we say that gravitation is universal we mean that
a. the Earth exerts gravitational force on objects on its surface
b. the Earth exerts a gravitational force on its moon and vice versa
c. the Earth, moon and sun exert gravitational forces on each other
d. all material objects in the universe exert gravitational forces on one another.
Question 4The creation of ____ require(s) that a young hot star (T 25,000 K) be relatively nearby.
a. Emission nebulae
b. HI regions
c. Molecular clouds
d. The cool gas of the interstellar medium
e. 21 cm radiation
Question 5Which of the following books of tabulated predicted planet positions was not based on uniform circular motion?
a. the Rudolphine Tables by Kepler
b. the Prutenic Tables based on Copernicus' model
c. the Alphonsine Tables based on Ptolemy's observations and calculations
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