AST 101 Chapter 3: Gravity and Motions

The ball will move faster if the person _______. (Select all that apply.)

Exerts a stronger force on the string. Lets out some string and exerts the same force.

Which fundamental force plays the most important role in shaping the structure of the Universe?

Gravity (Yes, Gravity plays the most important role in forming planets, stars, and galaxies, and in the interactions of galaxies and dark matter that affect large-scale structure and the expansion of the Universe.

A coconut falling from a tree is an example of ____________.

Newton's second law of motion (Yes! The force of gravity causes the apple to accelerate.)

While driving at high speed, you suddenly slam on the brakes. An unsecured bag on the seat will __________.

Slide forward due to its inertia (Yes, There is no force acting to stop the bag's motion.)

The green arrow pointing along the string represents.

The force on the ball from the string. (To keep the ball going in a circle, there must be a force acting to change the ball's direction.)

A rocket is in orbit around the Earth. This means _________ (Select all that apply.)

The force to hold the rocket in orbit is provided by gravity. If the rocket fires it engine and changes its V, its orbit will change. (Yes, if V changes F circular would no longer equal F and the orbit would change.)

A gun fire a dart, and the dart and the gun experience forces in opposite directions. This is an example of Newton's _______ Law

Third

Compared to being on the Earth, on Mars your _______.

Weight will be different and your mass the same (Yes! Weight depends on the pull of gravity. Mass depends on how much matter is in an object.)

If the gravitational force between Earth and the Moon were suddenly switched off, the Moon's motion __________.

Would be a straight line (Yes, in the absence of a force, inertia keeps the Moon moving straight.)

If quantity A is directly proportional to quantity B, then if B increases 10 times, A must increase ___________ times.

10

The gravitational force between two asteroids is 100 N. If the distance between them doubles, the gravitational force will be ___________.

25 N (Yes, the distance has doubled so the force is 1/4 as great/)

A planet with 9 times the mass and __________ times the radius of Earth will have the same surface gravity as Earth.

3 (Yes, 3 squared is 9, and this gives 9 over 9 in the equation.)

You apply a 12 N force to a 3 kg mass. The acceleration it produces is ____________ m/s.

4

Observing the effect of gravity between a planet and its moon can allow us to determine the planet's

Mass

If you are using the equation at the right to calculate the mass of a star based on the motion of a planet and if the units of Newton's constant G are M3 Kg-1 S-2, what should the units of D and P be?

Meters and Years (For the units to cancel correctly so that the final answer is in kilograms, D must be in meters and P in seconds. Meters and seconds

If one planet is larger (in size) than another, its surface gravity ______.

Might or might not be bigger, depending on it density.

If one planet is larger (In size) than another, its surface gravity _____.

Might or might not be bigger, depending on its density.

If two objects are accelerated to the same velocity, the more massive object requires ___________ force.

More (Yes, since A = Flm, for a bigger m you need a corresponding larger F to get the same A.)

An astronaut in space swings a ball on a string in a circle. If the string breaks, the ball with ________.

Move in a straight line (Yes, the ball's inertia will keep it moving in a straight line.)

The idea that a force exists between two bodies that depends on the product of their masses and the square of the distance between them was formalized by ________ and is known as the universal law of __________.

Newton Gravitation

Which idea or equation best explains the different accelerations (arrows) shown in the picture?

Newton's second law: a = F/M (Yes! The same force accelerates a smaller mass more.)

Two planets with the same mass orbit a Sun-like star. One has a semimajor axis three times as long as the other's. The force of gravity between the star and the closer planet ______ the force of gravity between the star and the farther planet.

Nine times stronger than (Yes, since the closer planet is 1/3 the distance of the farther one, the gravitational force is nine (3*2) times as much.)

Select the planet that would have the same surface gravity as the Earth.

One with nine times the mass and three times the radius. (Yes, G=M/R so the changes cancel out.)

The force to keep an object turning in a circle is given by F = M X V*2/D. You swing a ball on a string. The same force is required to swing the ball three times as fast (3V) at distance d as is required to swing it at speed V at _________ the distance.

One-ninth (Yes, V - 3V makes the force go up 9 times (V is squared and on top) D 1/9D would have the same effect (D is not squared and is on the bottom of the fraction.)

You release a ball that rolls downhill on a curving ramp. This is considered "Accelerated motion" because __________. (Select all that apply)

The ball's speed is changing (Yes, Acceleration produces a change in speed, direction or both.) The ball's direction is changing (Yes, Acceleration produces a change in speed, direction or both.)

A rocketship in space fires its engine. The force that accelerates it is from _________.

The reaction to rocket fuel exploding out the back of the ship (Yes! The force pushing on the ship forward is equal and opposite to the force accelerating the burning fuel out the back.)

Astronomers might use the modified version of Kepler's third to determine _________. (Select all that apply.)

The total mass of a binary star system. (Yes, the mass of the stars can be determined using Kepler's third law) The mass of a Kulper belt dwarf planet and its moon. (Yes! The mass of the planet and moon could be found using Kepler's third law.) The mass of a nearby star with planets (Yes! The planet's orbits can be used to find the mass of the star.)

Newton's ________ law of motion is that two interacting bodies produce a pair of equal and opposite forces.

Third

An orbit that is nine times farther from a black hole will have a circular velocity that is ____________ than the closer orbit.

Three times slower (Yes! If D increases by a factor of nine, V must decrease by /9=3.)

Newton's law of inertia states that a moving body maintains a constant ________, moving in a ____________ line, unless a ______ acts on it.

Velocity Straight Force

Astronauts sometimes train in water tanks because the buoyancy of water exerts a force that opposes the pull of the Earth's gravity. In the tank, the ______ of the astronauts and their equipment decreases, but the ______,, which affects how hard it is to move them, stays the same.

Weight Inertia

The ____ force is the fundamental force that gives the Universe its structure.

Gravitational (Yes, Gravity holds together astronomical bodies of all sizes, from planets to galaxies.)

For the same radius, the larger a planet's mass, the _______ the escape velocity.

Greater

The image demonstrates _________ (Select all that apply.)

How something can be forever "Falling" but not hit the Earth. "Newton's cannon", a thought experiment (Yes, Thought experiments can be useful ways to explore scientific problems.)

Ancient scientists developed incorrect models of the Solar System because ___________. (Select all that apply.)

Human perception does not sense the Earth's motion They didn't properly understand friction or gravity. (Early scientists misunderstood the role of friction and developed incorrect rules of motion.)

The tendency of a body at rest to remain at rest, or of a body moving in a straight line to remain moving in a straight line, is known as ___________.

Inertia

In the absence of any forces, what keeps an object moving at constant speed?

Inertia (Inertia is also the property that keeps a still object at rest.)

A car turns a corner, and the Moon orbits the Earth. There is more inertia overcome in changing the Moon's direction because _________.

It is much more massive (Yes the more mass, the more inertia)

Select all the choices that describe escape velocity.

It's the speed required to escape a body's gravity. It's equal to /2gm/r

The speed of an object is how fast i tmoves-how far it goes over a period of time. The velocity of an object is ________.

Its speed and the direction it travels.

The surface gravity of a planet with twice the mass and twice the radius of Earth will be _______ surface gravity of Earth.

Less than (Yes, the radius is squared but the mass isn't)

Select all that represent an object undergoing an acceleration.

A car breaking to a stop. (Any change in velocity is an acceleration.) A car turning a corner at 88 km/hr (A change in direction in an acceleration) A ball falling off a table (The falling ball is accelerated by gravity.)

Select the cases in which the object undergoes acceleration.

A car slowing down with the brakes on. (Any change in speed counts.) A leaf falling from a tree (The falling leaf is accelerated by gravity.) The Moon orbiting the Earth (Orbiting objects constantly change direction *They are accelerated*.)

Near the surface of the Earth, G = 9.8 m/s. At a height of 6400 km above the Earth's surface (one Earth radius), the acceleration of gravity would be ___________.

About one-quarter as much (Yes, 6400 KM above the surface is twice as far from the center, and R is squared.)

Select the cases that correctly describe orbiting objects.

As a result of Newton's second and third laws, the smaller body moves more. (You can show that the smaller body has a larger acceleration by equating the force of gravity formula to F = m x a for each object. When one object is very massive compared to the other object, the center of the balance point of the orbit can be inside the massive object. Two equally massive bodies orbit each other equally. (You can show that the accelerations that are equal by equating the force of gravity formula to F = m X a for each object.)

Select all of the statements that correctly describes the constant G in Newton's universal law of gravity.

G is essentially a conversion factor. The value of G is 6.67 x 10 Nm2/KG2 (A Newton *N* equal kg m/ s2) G is the same everywhere in the universe.

The ball will move faster if the person ________. (Select all that apply)

Exerts a stronger force on the string. Lets out some string and exerts the same force.

An astronaut floating in space throws a wrench, exerting a 20 N force. The astronaut __________.

Experiences a 20 N force in the opposite direction. (Yes, Newton's third law requires that the forces be equal and opposite.)

If all objects on the Earth are acted on by the force of gravity (Giving them weight), how is it that an object can remain stationary (be at constant velocity)?

For an object to remain stationary, gravity must be balanced by other forces. (Yes! No net force = No change in velocity

Newton's ______ law of motion states that the _______ acting on an object must be the product of the ________ and the acceleration of the object.

Second Force Mass

Reducing the separation of two bodies to one-fourth its original value will cause the gravitational force between them to become _______ times _________ (Select two choices.)

Stronger 16

________ is the term for the acceleration of gravity near a body's surface.

Surface Gravity

Two asteroids, R and S, orbit each other. R is 10 times the mass of S. Compared to the gravitational force exerted by R pulling S toward R, the gravitational force exerted by S pulling R toward S is ____________.

The Same (Yes! Gravity is between two masses and depends on both of them. Each pulls on the other with the same strength but in opposite directions (Newton's third law).