# 9-2 Gravity

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What did Newton discover about gravity? a. The equation for the force of gravity. b. The Newtonian synthesis. c. The law of universal gravitation. d. All of the above.
d. All of the above.
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What is the Newtonian synthesis? a. His alchemical work on alloys. b. His naming of the spectrum, ROYGBIV. c. The union of terrestrial laws and cosmic laws. d. His invention of calculus.
c. The union of terrestrial laws and cosmic laws.
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In what sense does the moon "fall"? a. The Moon does not "fall." Instead, it moves in a circle at a constant radius. b. The Moon "falls" away from Earth a bit on every orbit. c. It falls away from the straight path that it would follow if there were no forces acting on it. d. The Moon "falls" toward Earth a bit on every orbit.
c. It falls away from the straight path that it would follow if there were no forces acting on it.
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State Newton's law of universal gravitation in words. Then do the same with one equation. a. The force is proportional to the product of two masses and inversely proportional to the square of the distance between their centers: F ~ m1m2/d2. b. The force is proportional to the product of two masses and to the square of the distance between their centers: F ~ m1m2d2. c. The force is proportional to the product of two masses and inversely proportional to the distance between their centers: F ~ m1m2/d. d. The force is proportional to the product of two masses: F ~ m1m2.
a. The force is proportional to the product of two masses and inversely proportional to the square of the distance between their centers: F ~ m1m2/d2.
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What is the magnitude of the gravitational force between two 1-kg bodies that are 1 m apart? a. 6.67 × 10 -11 N. b. 10 N. c. 6.67 × 10 -11 kg. d. 1 kg.
b. 10 N
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When G was first measured by Henry Cavendish, newspapers of the time hailed his experiment as the "weighing Earth experiment." Why? a. With a known mass and the radius of the Earth, you can calculate the unknown mass of Earth. b. With a known mass and a scale, you can calculate the unknown mass of Earth. c. With a known mass, a scale, and the radius of Earth, you can calculate the unknown mass of Earth if you know G. d. By dropping a large lead sphere, you can measure the acceleration of Earth and find its mass.
c. With a known mass, a scale, and the radius of Earth, you can calculate the unknown mass of Earth if you know G.
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Why are occupants of the International Space Station considered weightless? a. The floor of the space station is made from cavorite, which blocks gravity. b. are so far from Earth that gravity is essentially zero. c. Centripetal force cancels gravity in the space station. d. They are in free fall.
d. They are in free fall.
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How does the thickness of paint sprayed on a surface change when the sprayer is held twice as far away? a. It is twice as thick. b. It is the same thickness. c. It is ¼ as thick. d. It is ½ as thick.
c. It is 1/4 as thick.
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Where do you weigh more: at the bottom of Death Valley or atop one of the peaks of the Sierra Nevada? Why? a. You weigh more in Death Valley because more atmosphere pushes down on you. b. You weigh more on the summit, because the higher you go, the harder you fall. c. You weigh more in Death Valley because you are closer to the center of Earth. d. You weigh more on the summit because the air buoys you up less.
c. You weigh more in Death Valley because you are closer to the center of the Earth.
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Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was accelerating upward? Downward? a. More compressed while accelerating upward and while accelerating downward b. More compressed while accelerating upward, but less compressed while accelerating downward c. Less compressed while accelerating upward and while accelerating downward d. Less compressed while accelerating upward, but more compressed while accelerating downward
b. More compressed while accelerating upward, but less compressed while accelerating downward.
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Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was moving upward at constant velocity? Downward at constant velocity? a. There would be no more compression and no more expansion for both upward and downward motion. b. Less compressed while moving upward and more compressed while moving downward c. More compressed while moving upward and while moving downward d. More compressed while moving upward and less compressed while moving downward
a. There would be no more compression and no more expansion for both upward and downward motion.
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When is your weight measured as mg? a. For a mass accelerating downward with an acceleration g b. For a mass near the surface of Earth in free fall c. For a non-accelerating mass near the surface of Earth d. For a mass accelerating upward with an acceleration g near the surface of Earth
c. For a non-accelerating mass near the surface of the Earth.
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Give an example of when your weight is greater than mg. Give an example of when your weight is zero. a. Your weight is greater than mg when you are in free fall. Your weight is zero when you are accelerating upward. b. Your weight is greater than mg when you are accelerating upward. Your weight is zero when you are in free fall. c. Your weight is greater than mg when you are on top of a mountain. Your weight is zero when you are in free fall. d. Your weight is greater than mg when you are accelerating downward. Your weight is zero when you are in free fall.
b. Your weight is greater than mg when you are accelerating upward. Your weight is zero when you are in free fall.
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Do tides depend more on the strength of gravitational pull or on the difference in strengths? Explain. a. Tides depend weakly on the difference and strongly on the strength. b. Tides depend on both the strength and the difference equally. c. Tides depend only on the strength. d. Tides depend only on the difference.
d. Tides depend only on the difference.
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Describe how the gravitational forces from the Sun and the Moon compare from one side of Earth to the other. a. The Sun exerts a stronger force on the side of Earth furthest from the Sun, and the Moon exerts a stronger force on the side nearest the Moon. b. The Sun exerts a stronger force on the side of Earth nearest the Sun, and the Moon exerts a stronger force on the side nearest the Moon. c. The Sun exerts a stronger force on the side of Earth furthest from the Sun, and the Moon exerts a stronger force on the side furthest from the Moon. d. The Sun exerts a stronger force on the side of Earth nearest the Sun, and the Moon exerts a stronger force on the side furthest from the Moon
b. The Sun exerts a stronger force on the side of the Earth nearest the Sun, and the Moon exerts a stronger force on the side nearest the Moon.
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Which has the higher tides: spring tides or neap tides? Why? a. Neap tides are higher, because the tides from the Moon and Sun add together. b. Spring tides are higher, because the tides from the Moon and Sun partially cancel. c. Neap tides are higher, because the tides from the Moon and Sun partially cancel. d. Spring tides are higher, because the tides from the Moon and Sun add together.
d. Spring tides are higher, because the tides from the Moon and the Sun add together.
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Do tides occur in the molten interior of Earth for the same reason that tides occur in the oceans? a. Yes, due to the strength of the gravitational force at the center of the core b. No, due to the strength of the gravitational force at the center of the core c.Yes, due to the difference in gravitational force across the core d. No, due to the difference in gravitational force across the core
c. Yes, due to the difference in gravitational force across the core.
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Why are all tides greatest at the time of a full Moon or new Moon? a. At full Moon and new Moon, the tides from the Moon and the Sun add because they are in line with Earth. b. At full Moon and new Moon, the tides from the Moon and the Sun partially cancel because they make a right angle with Earth. c. At full Moon and new Moon, the tides from the Moon and the Sun add because they make a right angle with Earth. d. At full Moon and new Moon, the tides from the Moon and the Sun partially cancel because they are in line with Earth.
a. At full Moon and new Moon, the tides from the Moon and the Sun add because they are in line with Earth.
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Would a torque on the Moon occur if the Moon were spherical, with both its center of mass and center of gravity in the same location? Why? a. Yes. The torque occurs even when the center of mass and the center of gravity are at the same location. b. No. The torque requires a distance between the center of mass and the center of gravity. c. No. The torque requires only a difference in force across the Moon. d. Yes. The torque requires a space between the center of mass and the center of gravity.
b. No. The torque requires a distance between the center of mass and the center of gravity.
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What is a gravitational field, and how can its strength be measured? a. It is a force field on a body with mass, with direction and magnitude equal to the inverse square of the distance to a test mass. b. It is a force field on any body with mass. Its strength is the force per unit mass on a test mass. c. It is a force field in empty space with direction and magnitude equal to the inverse square of the mass of a test mass. d. It is a force field with direction and magnitude at every point in space. It's strength is the force on a test mass.
b. It is a force field on any body with mass. Its strength is the force per unit mass on a test mass.
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What is the magnitude of the gravitational field at Earth's center? a. Zero N/kg b. 2g N/kg c. g/2 N/kg d. g N/kg
a. Zero N/kg
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For a planet of uniform density, how would the magnitude of the gravitational field halfway to the center compare with the field at the surface? a. Zero m/s2 b. g/2 N c. g/2 m/s2 d. g m/s2
c. g/2 m/s2
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What would the magnitude of the gravitational field be anywhere inside a hollow, spherical planet? a. A quarter of the surface value b. The same as the surface value c. Half the surface value d. Zero N/kg
d. Zero N/kg
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Newton viewed the curving of the path of a planet as being caused by a force acting on the planet. How did Einstein view the curved path of a planet? a. Moving in curved 4-dimensional spacetime b. Always at rest c. In a straight line called a geodesic d. In an ellipse
a. Moving in 4-dimensional spacetime.
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If Earth shrank, but there was no change in its mass, then what would happen to your weight at the surface? a. It would increase. b. It would decrease at first and then increase. c. It would decrease. d. It would stay the same.
a. it would increase.
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What happens to the strength of the gravitational field at the surface of a star that shrinks? a. It first increases and then it decreases. b. It decreases. c. It stays the same. d. It increases.
d. it increases.
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Why is a black hole invisible? a. A black hole is a black dwarf star. b. A black hole is surrounded by an opaque cloud of dust. c. A black hole is made of matter that absorbs all wavelengths of light. d. The escape velocity of the black hole is greater than the speed of light.
d. The escape velocity of the black hole is greater than the speed of light.
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Calculate the force of gravity on the 1-kg mass if it were 6.4×106 m above Earth's surface (that is, if it were two Earth radii from Earth's center).
F= 2.4 N
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Calculate the force of gravity between Earth (mass = 6.0×1024kg) and the Sun (mass = 2.0×1030 kg ). The average Earth-Sun distance is 1.5×1011 m .