# Mastering Astronomy Chapter 4 Answers

Flashcard maker : Lily Taylor
Which statement must be true in order for a rocket to travel from Earth to another planet?
It must attain escape velocity from Earth.
Compared to its angular momentum when it is farthest from the Sun, Earth’s angular momentum when it is nearest to the Sun is
the same
A car is accelerating when it is
going around a circular track at a steady 100 miles per hour.
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
To make a rocket turn left, you need to:
fire an engine that shoots out gas to the right
Which person is weightless during the activity shown?
Free falling person
Which of the following statements about the force attracting these two galaxies is true?
It is the same force that causes an apple to fall to the ground.
The diagram above shows a planet at four positions in its orbit. At which position does it have the greatest angular momentum?
The angular momentum is the same at all four points.
The diagram above shows a planet at four positions in its orbit. At which position does it have the greatest gravitational potential energy?
Farthest from the sun
The diagram above shows a planet at four positions in its orbit. At which position does it have the greatest total orbital energy? (Orbital energy is the sum of the planet’s kinetic and gravitational potential energy.)
The total orbital energy is the same at all four positions.
Which of the paths shown represent unbound orbits?
Moving away from the planet
Suppose you are aboard a rocket that is orbiting Earth in the low, circular orbit shown. If you want to escape from Earth and head to the Moon or Mars along the “escape” path shown, what do you need to do?
Fire the rocket engine in your direction of travel, so that you gain speed.
Which of the following correctly shows tidal bulges on Earth when the Moon is in the position shown?
there are two tidal bulges, one facing the Moon and one on the side of Earth opposite the Moon.
In which position(s) of the Moon do we experience the highest high tides?
1 & 3
In which position(s) of the Moon do we experience the lowest low tides?
1 & 3
Which of the following examples describes a situation where a car is experiencing a net force?
The car is making a gradual turn.
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
The gravitational potential energy of a contracting interstellar cloud
gradually transforms into other forms of energy.
If Earth were twice as far from the Sun, the force of gravity attracting Earth to the Sun would be
one-quarter as strong.
Which of the following represents a case in which you are not accelerating?
Suppose you drop a 10-pound weight and a 5-pound weight on the Moon, both from the same height at the same time. What will happen?
Why are astronauts weightless in the Space Station?
Because the Space Station is constantly in free-fall around the Earth
A net force acting on an object will always cause a change in the object’s
momentum
Suppose you are in an elevator that is traveling upward at constant speed. How does your weight compare to your normal weight on the ground?
it is the same
The planets never travel in a straight line as they orbit the Sun. According to Newton’s second law of motion, this must mean that
a force is acting on the planets
Suppose the Sun were suddenly to shrink in size but that its mass remained the same. According to the law of conservation of angular momentum, what would happen?
The Sun would rotate faster than it does now.
Suppose you kick a soccer ball straight up to a height of 10 meters. Which of the following is true about the gravitational potential energy of the ball during its flight?
The ball’s gravitational potential energy is greatest at the instant when the ball is at its highest point
Suppose you heat an oven to 400°F and boil a pot of water. Which of the following explains why you would be burned by sticking your hand briefly in the pot but not by sticking your hand briefly in the oven?
The water can transfer heat to your arm more quickly than the air.
Which of the following scenarios involves energy that we would typically calculate with Einstein’s formula E = mc 2?
A small amount of the hydrogen in of a nuclear bomb becomes energy as fusion converts the hydrogen to helium.
A rock held above the ground has potential energy. As the rock falls, this potential energy is converted to kinetic energy. Finally, the rock hits the ground and stays there. What has happened to the energy?
The energy goes to producing sound and to heating the ground, rock, and surrounding air.
Suppose that the Sun shrank in size but that its mass remained the same. What would happen to the orbit of the Earth?
Earth’s orbit would be unaffected.
Imagine another solar system, with a star of the same mass as the Sun. Suppose a planet with a mass twice that of Earth (2M Earth) orbits at a distance of 1 AU from the star. What is the orbital period of this planet?
one year
Imagine another solar system, with a star more massive than the Sun. Suppose a planet with the same mass as Earth orbits at a distance of 1 AU from the star. How would the planet’s year (orbital period) compare to Earth’s year?
The planet’s year would be shorter than Earth’s
Newton showed that Kepler’s laws are
natural consequences of the law of universal gravitation
Each of the following lists two facts. Which pair of facts can be used with Newton’s version of Kepler’s third law to determine the mass of the Sun?
Earth is 150 million km from the Sun and orbits the Sun in one year.
When space probe Voyager 2 passed by Saturn, its speed increased (but not due to firing its engines). What must have happened?
Saturn must have lost a very tiny bit of its orbital energy.
Suppose that a lone asteroid happens to be passing Jupiter on an unbound orbit (well above Jupiter’s atmosphere and far from all of Jupiter’s moons.) Which of the following statements would be true?
The asteroid’s orbit around Jupiter would not change, and it would go out on the same unbound orbit that it came in on.
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 (for example, the highest high tides)?
both new and full moons
Which of the following best explains why the Moon’s orbital period and rotation period are the same?
The Moon once rotated faster, but tidal friction slowed the rotation period until it matched the orbital period.
Compared to their values on Earth, on another planet your
mass would be the same but your weight would be different.
Consider the statement “There’s no gravity in space.” This statement is:
completely false
A planet with twice Earth’s mass orbiting at a distance of 1 AU from a star with the same mass as the Sun.
one year
A planet with the same mass as Earth orbiting at a distance of 1 AU from a star with four times the Sun’s mass.
6 months
Which person is weightless?
A child in the air as she plays on a trampoline.
If the Moon were closer to Earth, high tides would
be higher than they are now