Newton's First Law says a planet would fly off in a straight line if something were removed. What keeps it in its orbit?

The planet's own magnetic field locks it to the solar magnetic field Gravity from the Sun continuously pulls the planet inward, bending its path into a curve The planet's atmosphere creates drag against interplanetary space Dark matter forms a tube that guides the planet around its path

Newton's Second Law states F = ma. If a spacecraft has a mass of 2,000 kg and its engine provides a thrust force of 10,000 N, what is the spacecraft's acceleration?

0.2 m/s^2 2 m/s^2 5 m/s^2 20,000,000 m/s^2

Newton's Third Law says every action has an equal and opposite reaction. How does this principle make a rocket engine work?

The rocket engine pushes against air molecules in space Hot gas is expelled backward at high speed; the equal and opposite reaction pushes the rocket forward The rocket is pulled forward by the gravitational attraction of its destination Magnetic repulsion from the launch pad continues pushing the rocket through space

According to Newton's law of universal gravitation, if the distance between two objects doubles, how does the gravitational force between them change?

The force becomes two times weaker The force stays the same — gravity reaches infinitely far The force becomes four times weaker The force becomes eight times weaker

The gravitational constant G equals 6.674 x 10^-11 N m^2/kg^2. This number is extremely small. What does that tell us about gravity?

Gravity is the strongest of all forces, which is why it shapes the universe Gravity is by far the weakest of the four fundamental forces, but it dominates the cosmos because it is always attractive and acts over infinite range Gravity only exists in the solar system where G was measured Gravity is a push-pull force that alternates direction depending on mass

Earth's escape velocity is 11.2 km/s. The Moon's is only 2.4 km/s. Why is the Moon's escape velocity so much lower?

The Moon has no magnetic field, which would otherwise add to escape velocity The Moon is much less massive and smaller than Earth, so its gravitational pull is weaker and less energy is needed to escape it The Moon orbits Earth, so Earth's gravity reduces the effort needed to escape the Moon The Moon rotates more slowly, which reduces its escape velocity

The inverse square law means that Neptune (about 30 AU from the Sun) feels about 900 times less gravitational force from the Sun than Earth does. If Neptune has 17 times Earth's mass, what can we say about the Sun's gravitational force on Neptune compared to Earth?

The Sun's force on Neptune is zero because it is too far away The Sun pulls Neptune exactly as hard as it pulls Earth because Newton's force is equal on all planets The Sun still pulls on Neptune significantly because Neptune is much more massive than Earth, even though the force per kilogram is 900 times weaker at Neptune's distance Neptune's greater mass reverses the inverse square law so the force is actually stronger there

Escape velocity is the minimum speed needed to escape a gravitational field without further thrust. What happens to an object launched at exactly escape velocity?

It immediately stops at the edge of the gravitational field It travels at constant speed forever once past the atmosphere It slows down continuously but never quite stops — it escapes to infinity, arriving there with zero speed It enters orbit around the planet at the edge of the atmosphere

Newton's law of gravity is extremely accurate for planetary orbits, yet it breaks down in some situations. Where does it fail?

Newton's gravity fails whenever objects are outside the solar system Newton's gravity fails for objects smaller than an atom In very strong gravitational fields or at speeds close to the speed of light — Einstein's general relativity is needed in these cases Newton's gravity only works on Earth and fails completely in space

Two astronauts float in space far from any planet. Astronaut A has twice the mass of Astronaut B. According to Newton's Third Law, how do the gravitational forces they exert on each other compare?

Astronaut A pulls harder on Astronaut B because A is more massive Astronaut B pulls harder on Astronaut A because smaller objects always attract larger ones They pull on each other with exactly equal and opposite forces — Newton's Third Law always applies regardless of the masses involved There is no gravitational force between objects with no planet nearby

Earth's surface gravity is 9.8 m/s^2. If you traveled to a planet with twice Earth's mass but the same radius, what would the surface gravity be?

About 4.9 m/s^2 — half Earth's surface gravity About 9.8 m/s^2 — the same as Earth's, because the planet is the same size About 19.6 m/s^2 — twice Earth's surface gravity About 39.2 m/s^2 — four times Earth's surface gravity