Question 1

The time period between two successive passages of a planet past a particular star as seen from the Sun is its

Accepted Answer

A)  synodic period. 
B)  sidereal period. 
C)  precessional period. 
D)  rotational period.

Question 2

The force of gravity between two objects is proportional to the

Accepted Answer

A)  sum of their masses. 
B)  difference of their masses. 
C)  ratio of their masses. 
D)  product of their masses.

Question 3

The initial reason that the geocentric model for the solar system began to be discarded after the fifteenth century A.D. was that

Accepted Answer

A)  observations by spacecraft proved that all planets orbit the Sun. 
B)  the invention of the telescope provided observations that were in better agreement with a heliocentric model. 
C)  Isaac Newton was able to derive all planetary motion from one universal law of gravity. 
D)  the heliocentric model is conceptually simpler.

Question 4

Viewed from Earth, Mars is

Accepted Answer

A)  always above the ecliptic. 
B)  always below the ecliptic. 
C)  sometimes above and sometimes below the ecliptic. 
D)  always on the ecliptic.

Question 5

Suppose that a planet of the same mass as Earth were orbiting the Sun at a distance of 10 au. The gravitational force on this planet due to the Sun would be

Accepted Answer

A)  1/100 of the gravitational force the Sun exerts on Earth. 
B)  100 times the gravitational force the Sun exerts on Earth. 
C)  1/10 of the gravitational force the Sun exerts on Earth. 
D)  10 times the gravitational force the Sun exerts on Earth.

Question 6

Imagine a planetary system with a star and a single Earth-mass planet. Astronomers determine that the planet follows an elliptical orbit. What orbit does the star follow?

Accepted Answer

A)  It remains motionless, because it is so much more massive than the planet. 
B)  It follows an elliptical orbit with the center of mass of the system at one focus. 
C)  It remains motionless, because it is so far from the planet. 
D)  It follows an elliptical orbit with the planet at one focus.

Question 7

An inferior planet moves more or less directly toward Earth at greatest eastern elongation. What does this mean for an observer is watching the night-by-night motion of this planet against the background stars?

Accepted Answer

A)  The planet appears to remain stationary for a few days. 
B)  The planet appears to be moving at its fastest motion against the background. 
C)  The planet is invisible in the sky because it is moving toward Earth. 
D)  The planet's motion against the background will appear to be normal, that is, direct motion, because apparent motion is always constant in a circular orbit.

Question 8

The person who first showed that planetary orbits are ellipses was

Accepted Answer

A)  Copernicus. 
B)  Newton. 
C)  Galileo. 
D)  Kepler.

Question 9

The scientific method is a major force in science, and theories describing physical phenomena have been developed with the aim of ensuring that

Accepted Answer

A)  they agree with what we find in experiments and observations. 
B)  results from experiments can be adjusted to agree with carefully constructed theoretical ideals. 
C)  they agree with the wisdom of the ancients. 
D)  they are so good and our faith in them is so strong that we never need to test them against observations.

Question 10

A comet, originating in the solar system, is observed to have a hyperbolic orbit. What is MOST likely to have happened?

Accepted Answer

A)  The comet always had such an orbit. 
B)  The comet was deflected from an elliptical orbit by close encounters with other bodies in the solar system. 
C)  The comet was decelerated by solar radiation. 
D)  The comet's circular orbit was changed by gravitational radiation.

Question 11

The Greek mathematician Ptolemy devised a

Accepted Answer

A)  sundial. 
B)  geocentric model for the solar system. 
C)  heliocentric model for the solar system. 
D)  method to measure Earth's radius.

Question 12

An object is in an orbit caused by its gravitational attraction to the Sun. This orbit

Accepted Answer

A)  must be an ellipse. 
B)  must be a parabola. 
C)  must be a hyperbola. 
D)  might be an ellipse, a parabola, or a hyperbola.

Question 13

The original version of Kepler's third law, P2 = a3, applies to each of these orbits EXCEPT

Accepted Answer

A)  Mercury. 
B)  Jupiter. 
C)  the Moon. 
D)  Comet Halley.

Question 14

A person orbiting Earth in the Space Shuttle feels weightless because

Accepted Answer

A)  two forces are acting on her in opposite directions, so they cancel and produce the same effect as if no force at all were acting. 
B)  her mass is zero in space, and weight requires mass. 
C)  no forces act on her. 
D)  only one force (gravity) acts on her, but gravity also accelerates the shuttle, so the shuttle does not push up on her to create the feeling of weight.

Question 15

Why do astronomers need special units, in addition to the metric system of units such as meters and kilograms, to describe the universe?

Accepted Answer

A)  Distances and masses are very large, and representing them in metric units is cumbersome. 
B)  Metric units cannot represent correctly the curvature of space observed by astronomers. 
C)  Units used in the metric system are known to be insufficiently accurate to satisfy the precision needed in modern astronomy. 
D)  Metric units are too large to represent astronomical quantities with sufficient precision.

Question 16

In the years after Newton published his laws of motion, it was found that the observed positions of the planet Uranus did not match the predictions of Newton's theory. The reason for this turned out to be the

Accepted Answer

A)  perturbing effects of Jupiter and Saturn, whose masses at that time were not accurately known. 
B)  perturbing effect of Neptune, which at that time had not yet been discovered. 
C)  perturbing effect of Pluto, which at that time had not yet been discovered. 
D)  weakening of gravity with increasing distance from the Sun.

Question 17

Newton's second law states that

Accepted Answer

A)  force equals mass divided by acceleration. 
B)  force equals mass times acceleration. 
C)  weight equals force times acceleration. 
D)  acceleration equals force times mass.

Question 18

Suppose that an object is discovered moving around the Sun once every 120 years. Which of these paths is a possible orbit for this object?

Accepted Answer

A)  straight line 
B)  parabola 
C)  ellipse 
D)  hyperbola

Question 19

A person standing on bathroom scales sees a reading of 148 pounds. This person is acted on by

Accepted Answer

A)  no forces at all. 
B)  only one force (148 pounds, as shown by the reading on the scales). 
C)  only one force of 296 pounds (the sum of 148 pounds from Earth and 148 pounds from the scale). 
D)  two forces of equal size acting in opposite directions.

Question 20

How many moons of Jupiter did Galileo see?

Accepted Answer

A)  none; he was unable to see them with the unaided eye. 
B)  4 
C)  12 
D)  1

Exam 2: Gravitation and the Motion of the Planets