Question 1

Briefly explain why Earth feels a greater tidal force from the Moon than from the Sun, even though it feels a greater gravitational force from the Sun.

Accepted Answer

The answer of Briefly explain why Earth feels a greater...

Question 2

Give an example in which thermal energy might be converted to gravitational energy.

Accepted Answer

The answer of Give an example in which thermal energy...

Question 3

A planet is orbiting a star. Which of the following statements is true for the acceleration and gravitational forces experienced by the star and the planet?

Accepted Answer

The gravitational force between the star and the planet is equal in magnitude and opposite in direction (Newton's third law). However, due to the planet's smaller mass, its acceleration is much greater than that of the star (Newton's second law).

Question 4

State Newton's three laws of motion.

Accepted Answer

The answer of State Newton's three laws of motion....

Question 5

Give an example in which kinetic energy can be converted to thermal energy.

Accepted Answer

The answer of Give an example in which kinetic energy...

Question 6

If a gas cloud shrinks its gravitational potential energy is converted into

Accepted Answer

As the gas cloud shrinks, its particles move closer together, which causes an increase in kinetic energy and results in the production of thermal energy. Additionally, as the gas cloud heats up, it emits radiation in the form of electromagnetic waves, which accounts for the radiative energy produced during the shrinking process. Therefore, both thermal energy and radiative energy are generated and the correct choice is D. Choice A is incorrect because chemical energy is not involved in the process of gas cloud contraction. Choice B is incorrect because radiative energy is not the only form of energy produced during the shrinking process. Choice C is incorrect because although kinetic energy and sound waves are generated, thermal and radiative energy are also produced.

Question 7

Imagine another solar system, with a star of the same mass as the Sun. Suppose there is a planet in that solar system with a mass double that of Earth orbiting at a distance of 1 AU from the star. Thinking about Newton's version of Kepler's third law, what (approximately) is the orbital period of this planet? Explain your answer.

Accepted Answer

The answer of Imagine another solar system, with a star...

Question 8

Consider the elliptical orbit of a comet around the Sun. Where in its orbit does it have the largest amount of total orbital energy?

Accepted Answer

The answer of Consider the elliptical orbit of a comet...

Question 9

Under what conditions is an object weightless?

Accepted Answer

The answer of Under what conditions is an object weightless?...

Question 10

Suppose it takes 6 seconds for a watermelon to fall to the ground after being dropped from a tall building. If there were no air resistance, so that the watermelon would fall with the acceleration of gravity, about how fast would it be going when it hit the ground?

Accepted Answer

The answer of Suppose it takes 6 seconds for a...

Question 11

Imagine a Star Wars type spaceship in orbit around a planet. Its engine suffers a severe malfunction, and explodes. What is the most physically realistic depiction of this event?

Accepted Answer

In orbit, objects are constantly falling towards the planet, but they are also moving horizontally fast enough to miss it. If the spaceship were to explode, the pieces would continue to follow the same orbit, just like debris from a satellite collision would. Option A is not physically realistic because the spaceship would not begin to sink down into the planet like a sinking aircraft carrier. Option C is also not very realistic since there is no oxygen in space to sustain a fire, but there would be a brief flash of light as the explosion occurred.

Question 12

As an interstellar cloud of hydrogen gas shrinks in size, its rate of rotation

Accepted Answer

As the cloud shrinks in size, its moment of inertia decreases, which means that to conserve its angular momentum, it must increase its rate of rotation. This is known as the conservation of angular momentum, which states that the total angular momentum of a system remains constant unless acted upon by an external torque. Therefore, the rate of rotation of the cloud must increase.

Question 13

If a gas cloud shrinks, it

Accepted Answer

According to the law of conservation of angular momentum, as the gas cloud shrinks and its radius decreases, the angular velocity (spin) must increase to conserve the total angular momentum. Therefore, the gas cloud would spin faster.

Question 14

As an interstellar cloud of hydrogen gas shrinks in size, its temperature increases,

Accepted Answer

When an interstellar cloud of hydrogen gas shrinks in size due to the gravity, the potential energy of the system is converted into kinetic energy, which further increases the temperature of the gas molecules, causing them to move faster. This increases the thermal energy, which eventually gets converted into radiative energy as the cloud heats up and emits radiation. Therefore, option A is the best choice.

Question 15

Consider the elliptical orbit of a comet around the Sun. Where in its orbit is the comet moving the fastest?

Accepted Answer

According to Kepler's Second Law, a planet or comet moves faster when it is closer to the Sun, and slower when it is farther away. Therefore, when the comet is closest to the Sun, it will be moving the fastest in its elliptical orbit.

Question 16

A popular end for many cartoon characters is to fall into a "bottomless pit" in which the unfortunate character will fall forever. Consider the space shuttle in orbit around the Earth. Argue that there is a strong analogy between the cartoon "bottomless pit" and the orbital motion of the shuttle.

Accepted Answer

The answer of A popular end for many cartoon characters...

Question 17

Explain what synchronous rotation is. What is it caused by? Give an example.

Accepted Answer

The answer of Explain what synchronous rotation is. What is...

Question 18

How does a rocket launch upwards? Choose the statement that best describes why a rocket goes up.

Accepted Answer

A rocket launches upwards by expelling gas downwards from its engines. This creates a reaction force that propels the rocket upwards, according to Newton's third law of motion. The force of the gas pushing downwards is transferred to the rocket, which pushes upwards as a result.

Question 19

Suppose a satellite is in a low-Earth orbit. Is it possible that the satellite will eventually fall to the ground? Why or why not?

Accepted Answer

The answer of Suppose a satellite is in a low-Earth...

Question 20

The astronauts feel weightless in the International Space Station, which orbits the Earth once every 90 minutes. Why?

Accepted Answer

The astronauts feel weightless in the International Space Station because they are falling around the Earth. In space, there is still gravity, but the ISS and everything inside it are in a constant state of free fall towards the Earth, giving the sensation of weightlessness. The speed of the ISS helps to maintain this perpetual state of free fall.

Quiz 4: Making Sense of the Universe: Understanding Motion, Energy, and Gravity