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ASTRO Chapter 4
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Gravity
Terms in this set (72)
Which of the following is an example in which you are traveling at constant speed but not at constant velocity?
driving around in a circle at exactly 100 km/hr
Standing on the surface of the Earth you drop a rock down a well and it falls for 5 seconds before hitting the bottom. How fast is it moving when it hits the bottom of the well? Neglect air resistance.
50 m/s
Momentum is defined as
mass times velocity
If an object's velocity is doubled, its momentum is
doubled
As long as an object is not gaining or losing mass, a net force on the object will cause a change in
velocity.
If your mass is 60 kg on Earth, what would your mass be on the Moon?
60 kg
In which of the following cases would you feel weightless?
while falling from a roof
What would happen if the Space Shuttle were launched with a speed greater than Earth's escape velocity?
It would travel away from Earth into the solar system.
Speed and velocity are the same thing.
False
The acceleration of gravity on Earth is approximately 10 m/s2 (more precisely, 9.8 m/s2). If you drop a rock from a tall building, about how fast will it be falling after 3 seconds?
30 m/s
Suppose you lived on the Moon. Which of the following would be true?
Your weight would be less than your weight on Earth, but your mass would be the same as it is on Earth.
Choose the correct description of an object that is accelerating?
A car going around a circular track at a steady 100 miles per hour.
Compared to their values on Earth, on another planet your
mass would be the same but your weight would be different
Suppose you are in an elevator. As the elevator starts upward, its speed will increase. During this time when the elevator is moving upward with increasing speed, your weight will be __________.
greater than your normal weight at rest
Suppose you are in an elevator that is moving upward. As the elevator nears the floor at which you will get off, its speed slows down. During this time when the elevator is moving upward with decreasing speed, your weight will be __________.
less than your normal weight at rest
When you are standing on a scale in an elevator, what exactly does the scale measure?
the force you exert on the scale
Suppose you are in an elevator car when the elevator cable breaks. Which of the following correctly describes what happens and why?
You float weightlessly within the elevator car because you and the elevator both begin to accelerate downward at the same rate.
Suppose an object is moving in a straight line at 50 miles/hr. According to Newton's first law of motion, the object will?
continue to move in the same way until it is acted upon by a force.
Newton's second law of motion tells us that the net force applied to an object equals its
mass times acceleration.
How does the Space Shuttle take off?
Hot gas shoots out from the rocket and, by conservation of momentum, the shuttle moves in the opposite direction.
The fact that the Voyager spacecraft continues to travel out of the solar system, even though its rockets have no fuel, is an example of?
Newton's first law of motion.
Which of the following examples describes a situation where a car is experiencing a net force?
The car is making a gradual turn
Consider the statement "There's no gravity in space." This statement is:
Completely false.
What quantities does angular momentum depend upon?
mass, velocity, and radius
A skater can spin faster by pulling her arms closer to her body or spin slower by spreading her arms out from her body. This is due to?
conservation of angular momentum.
Which of the following is not a conserved quantity?
radiation
Radiative energy is?
energy carried by light.
Gasoline is useful in cars because it has?
chemical potential energy.
Absolute zero is?
0° Kelvin
What does temperature measure?
the average kinetic energy of particles in a substance
In the formula E = mc2, what does E represent?
the mass-energy, or potential energy stored in an object's mass
Considering Einstein's famous equation, E = mc2, which of the following statements is true?
A small amount of mass can be turned into a large amount of energy.
The amount of gravitational potential energy released as an object falls depends on?
its mass and the distance it falls, as well as the rate of gravitational acceleration.
Which of the following scenarios correctly demonstrates the transformation of mass into energy as given by Einstein's equation, E = mc2?
When hydrogen is fused into helium, whether in the Sun or in a nuclear bomb, the mass difference is turned into energy.
The ultimate source of energy that powers the Sun is?
mass energy of hydrogen fusing into helium.
Which of the following statements correctly describes the law of conservation of energy?
The total quantity of energy in the universe never changes.
Where does the energy come from that your body uses to keep you alive?
It comes from the foods you eat.
When a rock is held above the ground, we say it has some potential energy. When we let it go, it falls and we say the potential energy is converted to kinetic energy. Finally, the rock hits the ground. What has happened to the energy?
The energy goes to producing sound and to heating the ground, rock, and surrounding air
When energy is converted from one form to another, a tiny amount is inevitably lost.
False
If you are driving at 30 miles per hour and increase your speed to 60 miles per hour, you quadruple your kinetic energy.
True
Of the temperature ranges below, which range represents the smallest range of actual temperature?
50-100° Fahrenheit
Which object has the most kinetic energy?
a 2-ton truck moving 90 km/hr
According to the universal law of gravitation, the force due to gravity is
inversely proportional to the square of the distance between objects.
According to the universal law of gravitation, if you triple the distance between two objects, then the gravitational force between them will
decrease by a factor of 9.
According to the universal law of gravitation, if you double the masses of both attracting objects, then the gravitational force between them will
increase by a factor of 4
According to what we now know from Newton's laws, which of the following best explains why Kepler's second law is true?
A planet's angular momentum must be conserved as it moves around its orbit
The center of mass of a binary star system is
the balance point of the system, around which the two objects would revolve.
The mass of Jupiter can be calculated by
measuring the orbital period and distance of one of Jupiter's moons.
The Moon is constantly falling toward Earth.
True
The center of mass for Earth orbiting the Sun lies inside the Sun.
True
There is no gravity in space.
False
Doubling the distance between two objects halves the gravitational force between them.
False
Process of Science: Gravity only affects very massive objects and we can therefore only test theories about it when looking at the orbits of planets.
False
Why is Newton's version of Kepler's third law so useful to astronomers?
It can be used to determine the masses of many distant objects.
If Earth were twice as far from the Sun, the force of gravity attracting Earth to the Sun would be:
one-quarter as strong.
According to the law of universal gravitation, what would happen to Earth if the Sun were somehow replaced by a black hole of the same mass?
Earth's orbit would not change.
Consider Earth and the Moon. As you should now realize, the gravitational force that Earth exerts on the Moon is equal and opposite to that which the Moon exerts on Earth. Therefore, according to Newton's second law of motion __________.
the Moon has a larger acceleration than Earth, because it has a smaller mass
The allowed shapes for orbits under the force of gravity are
ellipses, parabolas, and hyperbolas
Which of the following best describes the origin of ocean tides on Earth?
Tides are caused by the difference in the force of gravity exerted by the Moon across the sphere of the earth.
At which lunar phase(s) are tides most pronounced (e.g., the highest high tides)?
both new and full Moons
At which lunar phase(s) are tides least pronounced (e.g., the lowest high tides)?
both first and third quarters
The Moon is slowly moving away from Earth.
True
Most people are familiar with the rise and fall of ocean tides. Do tides also affect land?
Yes, though land rises and falls by a much smaller amount than the oceans.
Any particular location on Earth experiences __________.
two high tides and two low tides each day
One tidal bulge faces toward the Moon because that is where the gravitational attraction between Earth and the Moon is strongest. Which of the following best explains why there is also a second tidal bulge?
The second tidal bulge arises because gravity weakens with distance, essentially stretching Earth along the Earth-Moon line.
You have found that tides on Earth are determined primarily by the position of the Moon, with the Sun playing only a secondary role. Why does the Moon play a greater role in causing tides than the Sun?
because the gravitational attraction between Earth and the Moon varies more across Earth than does the gravitational attraction between Earth and the Sun
As a giant cloud of gas collapses due to gravity, you would expect its rate of rotation to
increase
Which of the following represents a change from potential energy to kinetic energy?
A rock starting from rest on a high cliff, then moving faster and faster as it falls.
Suppose two objects are attracting each other gravitationally. If you double the distance between them, the strength of their gravitational attraction __________.
decreases by a factor of 4
Tidal forces on Earth are causing
the Earth to slow down its rotation rate
We only see one face of the Moon from Earth because
the Moon is already tidally locked to the Earth.
In considering the Earth-Moon system we find
There are tidal forces on the Moon caused by the Earth, there are tidal forces on the Earth and Moon caused by the Sun, but the Sun's tidal influence is less than the Earth's on the Moon or the Moon's on the Earth, There are tidal forces on the Earth caused by the Moon
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