The Essential Cosmic Perspective, 8e (Bennett et al.)
Chapter 4 Making Sense of the Universe: Understanding Motion, Energy, and Gravity
4.1 Multiple Choice Questions
1) What is the acceleration of gravity at the surface of Earth?
A) 9.8 m/s2 downward
B) 9.8 m/s downward
C) 9.8 km/s2 downward
D) 9.8 m2/s downward
E) 9.8 km/s downward
2) If an object’s velocity is doubled, its momentum is
A) halved.
B) unchanged.
C) doubled.
D) quadrupled.
E) dependent on its acceleration.
3) As long as an object is not gaining or losing mass, a constant force applied to an object for a
period of time will result in a change in
A) acceleration.
B) direction.
C) weight.
D) speed.
E) velocity.
4) If your mass is 60 kg on Earth, what would your mass be on the Moon?
A) 10 lb
B) 10 kg
C) 50 kg
D) 60 kg
E) 60 lb
5) You are standing on a scale in an elevator. You notice your weight suddenly decreases and
remains decreased. What do you conclude?
A) The elevator is accelerating upwards.
B) The elevator is moving at a constant velocity upwards.
C) The elevator is accelerating downwards.
D) The elevator is moving at a constant velocity downwards.
6) What would happen if a rocket were launched with a speed greater than Earth’s escape
velocity?
A) It would travel away from Earth into the solar system.
B) It would travel in a higher orbit around Earth.
C) It would take less time to reach its bound orbit.
D) It would orbit Earth with a faster velocity.
E) It would be in an unstable orbit.
7) Suppose an object is moving in a straight line at 70 km/hr. According to Newton’s first law of
motion, the object will
A) continue to move in the same way forever, no matter what happens.
B) continue to move in the same way until it is acted upon by a force.
C) eventually slow down and come to a stop.
D) continue to move in a straight line forever if it is in space, but fall to the ground if it is on
Earth.
8) How does a rocket launched into space take off?
A) Its rocket engines push against the launch pad, propelling the rocket upwards.
B) By converting mass-energy to potential energy.
C) By achieving lift from its wings in the same way that airplanes do.
D) Hot gas shoots out from the rocket and, through the conservation of momentum, the rocket
moves in the opposite direction.
E) The hot rocket exhaust expands the air beneath the shuttle, propelling it forward.
9) Earth is farthest from the Sun in July and closest to the Sun in January. During which
Northern Hemisphere season is Earth moving fastest in its orbit?
A) winter
B) spring
C) summer
D) fall
10) The fact that Voyager 10 continues to speed out of the solar system even though its rockets
have no fuel, is an example of
A) Newton’s first law of motion.
B) Newton’s second law of motion.
C) Newton’s third law of motion.
D) the universal law of gravitation.
E) none of the above
11) Changing the orbit of a spacecraft by firing thrusters is an example of
A) Newton’s first law of motion.
B) Newton’s second law of motion.
C) Newton’s third law of motion.
D) the universal law of gravitation.
E) none of the above
12) What quantities does angular momentum depend upon?
A) mass and velocity
B) mass, velocity, and radius
C) force and radius
D) force, velocity, and radius
E) momentum and angular velocity
13) Which of two bowling balls accelerate faster during their fall from the same height? Assume
the bowling balls are identical, except for their mass.
A) The heavier bowling ball accelerates faster.
B) They both fall with the same acceleration.
C) The lighter bowling ball accelerates faster.
14) How would you test the effect of an object’s mass on its acceleration by gravity?
A) Drop two balls of different mass from the same height.
B) Drop two balls of the same mass, but from different heights.
C) Drop two balls of different mass from different heights.
15) Considering Einstein’s equation relating mass and energy, E = mc2, which of the following
statements is true?
A) Mass can be turned into energy, but energy cannot be turned back into mass.
B) It takes a large amount of mass to produce a small amount of energy.
C) A small amount of mass can be turned into a large amount of energy.
D) You can make mass into energy if you can accelerate the mass to the speed of light.
E) One kilogram of mass represents 1 joule of energy.
16) The long-term source of energy that powers the Sun is
A) chemical potential energy of hydrogen burning into helium.
B) mass energy of hydrogen fusing into helium.
C) gravitational potential energy of the contraction of the gas cloud that formed the Sun.
D) kinetic energy of the orbital motion of the Sun.
E) thermal energy of the hydrogen atoms in the Sun.
17) If an interstellar gas cloud shrank in size, what does the law of conservation of angular
momentum predict will happen? It will
A) heat up.
B) slow down in its rotation.
C) cool off.
D) continue shrinking.
E) rotate faster.
18) Where does the energy come from that your body uses to keep you alive?
A) It is produced from the radiative energy of the Sun on your skin.
B) It comes from the foods you eat.
C) It comes from the water you drink.
D) It is in the air that you breathe.
E) It is created during the time that you rest or sleep.
19) According to the universal law of gravitation, the force due to gravity is
A) directly proportional to the square of the distance between objects.
B) inversely proportional to the square of the distance between objects.
C) directly proportional to the distance between objects.
D) inversely proportional to the distance between objects.
E) not dependent on the distance between objects.
20) The force of gravity is an inverse square law. This means that if you double the distance
between two large masses the gravitational force between them
A) also doubles.
B) strengthens by a factor of 4.
C) weakens by a factor of 4.
D) weakens by a factor of 2.
E) is unaffected.
21) According to the universal law of gravitation, if you double the masses of both attracting
objects, then the gravitational force between them will
A) not change at all.
B) increase by a factor of 2.
C) decrease by a factor of 2.
D) increase by a factor of 4.
E) decrease by a factor of 4.
22) If the Earth rotated once every 48 hours, and everything else was the same, which of the
following statements would NOT be true?
A) High tide would happen less frequently.
B) The length of the year would be longer.
C) The daytime temperatures would be higher on average.
D) There would still be summer and winter in the temperature zones.
E) The length of a day would be longer.
23) Suppose you drop a feather and a hammer on the Moon from the same height at the same
time. What will happen?
A) The feather will hit the ground first.
B) They will hit the ground at the same time.
C) The hammer will hit the ground first.
D) They will float in space because of the lack of gravity on the Moon.
24) The approximate mass of Jupiter can be calculated by
A) measuring the orbital period and distance of Jupiter’s orbit around the Sun.
B) measuring the orbital period and distance of one of Jupiter’s moons.
C) measuring the orbital speed of one of Jupiter’s moons.
D) knowing the Sun’s mass and measuring how Jupiter’s speed changes during its elliptical orbit
around the Sun.
E) knowing the Sun’s mass and measuring the average distance of Jupiter from the Sun.
25) Gravity is an inverse square law in distance. Therefore, if the distance between two masses is
decreased by a factor of 4, the gravitational force between those two masses
A) increases by a factor of 16.
B) increases by a factor of 4.
C) increases by a factor of 2.
D) decreases by a factor of 4.
E) decreases by a factor of 16.
26) At which lunar phase(s) are tides least pronounced (e.g., the lowest high tides)?
A) first quarter
B) new moon
C) full moon
D) both new and full moons
E) both first and third quarters
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27) Newton’s second law states: sum of forces = mass × acceleration. According to this, what
property can you determine if you observe the acceleration of an object with a known mass?
A) the sum total of all forces acting on the object
B) the value of a single force acting on the object
C) the current velocity of the object
D) the current location of the object
28) Newton’s second law states: sum of forces = mass × acceleration. If a known force was
applied to an object with a known mass, how would you predict that object’s acceleration?
A) acceleration = mass × sum of forces
B) acceleration = mass / sum of forces
C) acceleration = sum of forces / mass
D) Newton’s second law is irrelevant for solving this problem.
29) The force due to gravity between two objects can be described using the equation
Fg = G M1 M2 / d2. In this equation, what does d represent?
A) the universal gravitational constant
B) the density of the smaller object
C) the distance between the two objects
30) The force due to gravity between two objects can be described using the equation
Fg = G M1 M2 / d2. In this equation, what does G represent?
A) the universal gravitational constant
B) the density of the smaller object
C) the distance between the two objects
31) He realized the laws of gravity applied to objects in space and on the Earth.
A) Newton
B) Copernicus
C) Kepler
D) Galileo
32) The force due to gravity between two objects can be described using the equation
Fg = G M1 M2 / d2. According to this equation, if the distance between two objects increases,
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 distance.
33) Which of the following shapes is not an allowed trajectory of an undisturbed object around a
star?
A) a hyperbola
B) a parabola
C) a spiral
D) an ellipse
34) If the Sun instantaneously turned into a black hole of one solar mass, what would happen to
the Earth?
A) It would continue to orbit the black hole.
B) It would gradually spiral into the black hole.
C) It would be ejected into outer space.
D) It would be sucked into the black hole.
35) Newton’s version of Kepler’s third law states: p2 = × a3
In this equation, what does a represent?
A) the orbital period
B) the average distance between the two objects
C) the masses of the two objects
D) the universal gravitational constant
36) As a comet passes by on its closest approach to the Sun, what can we say about how the sum
of its potential and kinetic energy has changed since it was at its maximum distance?
A) The sum has not changed.
B) The sum has decreased.
C) The sum has increased.
D) The sum is equal to the universal gravitational constant.
37) Newton’s version of Kepler’s third law states: p2 = × a3
In this equation, what does G represent?
A) the orbital period
B) the average distance between the two objects
C) the masses of the two objects
D) the universal gravitational constant
38) Newton’s version of Kepler’s third law states: p2 = × a3
According to this, what observational information does one need in order to calculate the
combined mass of a planet and its moon?
A) the orbital period and the density of the two objects
B) the average distance between the two objects and the orbital period
C) the radius of the two planets in meters and the average distance between them
D) It is impossible to determine the mass of any astronomical object.
39) Newton’s version of Kepler’s third law states: p2 = × a3
Solve this equation to find the combined mass of a planet and its satellite, given the orbital
period and average separation.
A) M1 + M2 = 4Gπ2 ×
B) M1 + M2 = ×
C) M1 + M2 = ×
D) M1 + M2 = ×
40) When is a comet’s orbital angular momentum at its maximum?
A) when the comet is close to the Sun
B) when the comet is far away from the Sun
C) Its angular momentum does not change.
41) When is a comet’s orbital speed at its maximum?
A) when it is closest to the Sun
B) when it is farthest from the Sun
C) Its orbital speed does not change.
42) If a spinning star suddenly gets bigger in diameter, what happens to its rotation rate?
A) It increases.
B) It is unaffected.
C) It decreases.
43) Consider the elliptical orbit of a comet around the Sun. Where in its orbit does it have the
largest amount of total orbital energy?
A) when it is farthest from the Sun
B) when it is closest to the Sun
C) It always has the same total orbital energy.
4.2 True/False Questions
1) When a body of water on the rotating Earth passes through its closest point to the Moon, the
Moon causes a high tide to occur for that body of water, and this happens once per day.
2) The Moon is constantly falling toward Earth.
3) If you triple the mass of fusion material in a hydrogen bomb, you triple the amount of energy
it will generate.
4) When energy is converted from one form to another, a tiny amount is inevitably lost.
5) Kepler deduced his laws of planetary motion once Newton had published his universal law of
gravitation.
6) There is no gravity in space.
7) Moving two objects 10 times closer to each other will increase their gravitational attraction
100 times.
8) The escape velocity from Earth is greater for larger rockets than for smaller ones.
9) Tidal friction caused by Earth’s stretching from the Moon’s gravity is gradually slowing down
the rotation of Earth.
10) The Moon is slowly moving away from Earth.
11) Unbound orbits have more orbital energy than bound orbits.
12) When you experience a downward gravitational force from Earth, Earth likewise experiences
an upward gravitational force from you. The second force will be substantially weaker.
13) A spacecraft requires a propulsion system such as a rocket engine in order to be able to
continually move through space.
14) When you throw a ball straight up in the air at one speed, it will return to you at a faster
speed because it will have been accelerated downward by gravity.
15) By observing the orbital period of a planet’s moon, and measuring the distance between the
planet and the moon, one may determine the mass of the moon.
16) Thermal energy is a form of potential energy.
17) On a hot day, air particles move around faster than on a cold day.
18) Earth’s tidal forces acting on the Moon have caused one side of the Moon to be constantly
facing Earth.
4.3 Process of Science Questions
1) Do Things We Cannot Directly Detect Exist? In the early part of the 20th century, physicists
experimentally discovered that a certain type of radioactive decay did not seem to conserve
either energy or momentum. These experiments were “explained” by postulating the existence of
an undetected (and potentially undetectable) particle, dubbed the neutrino, that carried away the
missing energy and momentum. It was argued that neutrinos interacted so weakly with matter
that they were extremely hard to detect. If you were a scientist at this time, how would you
evaluate the reasonableness this solution given Occam’s razor?
2) Hallmarks of a Scientific Theory: All great scientific theories explain existing observations,
unify and extend existing concepts, and make new and novel predictions that can be
experimentally tested. Using Newton’s postulate of universal gravitation as a case study,
explicitly demonstrate how it satisfies each of these criteria.
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3) Argument by Analogy: A friend of yours is convinced of the influence of the Moon on
everyday human affairs. He cites a supposed correlation between crime and the occurrence of a
full moon as proof. He even speculates that the gravitational influence of the Moon is the
mechanism by noting that it is the gravitational pull of the Moon that causes the tides. “After
all”, he argues, “as over half a human’s weight is water, the Moon must affect the flow of blood
in human beings!” How would you explain to your friend that this analogy, between the ocean
tides and water in the human body, is profoundly flawed. Are there any alternate explanations for
a link between moon phase and crime?
4) Using equations: The force due to gravity between two objects can be described using the
equation 2. How would one use Newton’s second law to setup an equation one
could use to find the gravitational acceleration experienced by an isolated astronaut 10,000 km
from the Earth’s center?
5) Conservation laws: One powerful way to solve physics problems is to apply conservation
laws. Here are two examples: 1) Assume you determined the amount of walking, running, etc.
you did daily, and you knew the associated amounts of energy you expended. You also knew the
energy content in kilocalories of your meals. How would you use the Conservation of Energy to
plan a daily diet?
2) Can a bullet stop a hardball? Suppose you shot a rifle bullet into an oncoming hardball and the
bullet somehow lodged inside the ball. a) Which conservation law would you apply to the
problem and how would you solve it? b) Solve the problem assuming the bullet’s mass and
velocity are 10 gm and 1000 m/s, and the baseball’s mass and velocity are 147 gm and 34 m/s
(76 mph).