Astronomy Chapter 4

Suppose that a planet of 10 times the mass of Earth were orbiting the Sun at the same distance as Earth (1 AU). The gravitational force on this planet due to the Sun would be

10 times that on Earth due to the Sun.

The law of gravitation expounded by Newton for the force F between two objects of masses M and m with separation (between centers) of R is given, with G being a constant, by

F = GMm/R^2

The phenomenon of parallax is the

change in apparent position of a nearby object as the observer moves.

If you drop an object near Earth's surface it will have an acceleration of 9.8 m/s^2. If, instead, you throw the object downward, its acceleration (after it leaves your hand) will be

9.8 m/s^2

Suppose that a planet of the same mass as Earth were orbiting the Sun at a distance of 10 AU. The gravitational force on this planet due to the Sun would be

1/10 of the gravitational force the Sun exerts on Earth.

I have a massive purple object in my laboratory. If I were to take it to the Moon, which of its characteristics will be guaranteed to change?

weight

Which of the following four objects or persons is not accelerating?

an olympic swimmer exerting considerable force to maintain a constant speed in a straight line through the water

According to Newton's second law of motion, an object acted on by a constant force

moves with constant acceleration.

Earth exerts a force on you as you stand on its surface. What is the size of the force exerted on Earth by you, when compared to the above force?

the same

An unbalanced force acting on an object will always cause it to change its

speed or its direction of travel or both.

The eccentricity of a planet's orbit describes

its shape compared to that of a circle.

Two spaceships that have different masses but rocket engines of identical force are at rest in space. If they fire their rockets at the same time, which ship will speed up fastest?

the one with the lowest mass

If a planet moves around the Sun in a circular orbit, how many forces act on it?

one force toward the Sun

A certain object at rest on the surface of Earth has a weight of 49 Newtons. Its mass is, therefore,

5.0 kilograms.

According to Newton's first law,

if no force is acting on an object, then the object's speed and direction of travel will both be constant.

Spring tides occur

twice a month, at full and new moon

To specify an object's velocity completely, we need to specify

its speed and direction of travel.

Acceleration of a moving body is defined as the rate of change of

velocity with time.

Two objects of different mass when dropped by an astronaut on the Moon have

the same acceleration.

In which direction would Earth move if the Sun's gravitational force were suddenly removed from it?

in a straight line along a tangent to its circular orbit

A force can give a certain mass a certain acceleration. If I double the force and double the mass, the acceleration of this object will be

the same as the original acceleration.

On the Moon, where gravity is 1/6 of that on Earth, which of the following activities would an astronaut not find easier to carry out?

slowing down and stopping

You throw a ball straight up in the air. At its highest point the ball's

acceleration is not zero but its velocity is zero.

Kepler's second law states that a planet moves fastest when it

is closest to the Sun

When observing planetary motions from Earth, the phrase "retrograde motion" refers to

a slow westward motion of the planet from night to night against the background stars.

The water on the side of Earth that faces away from the Moon experiences

a high tide because the Moon in effect pulls the solid Earth out from under the water on the far side.

How many "tidal bulges" are there on Earth, due to the Moon's gravitational pull?

two, one facing (almost) directly toward the Moon and one facing (almost) directly away from the Moon

A major theme of Ancient Greek philosophy was that stars and planets in the sky

followed patterns that could be described logically

A planet's sidereal year is different from its synodic year because the

Earth moves

Kepler's first law states that the orbit of a planet about

the Sun is an ellipse with the Sun at one focus.

Which one of the following statements describes the Newtonian understanding of the mechanics of the solar system?

The natural motion of the planets is motion in a straight line. They are prevented from straight line motion by the gravitational force of the Sun.

The strength of gravity on Mars is about 40% of that on Earth. If you were to visit Mars, what would happen to your mass and weight compared to when you were on Earth?

Your mass would be the same but your weight would be less.

To which of these phenomena do Newton's laws of motion not apply?

a beam of light traveling between the Sun and Earth

Which of the following statements is a correct version of Newton's third law?

Whenever object A exerts a force on some other object B, B must exert a force of equal magnitude on A in the opposite direction.

An object orbiting the Sun in a circle can be said to be

always accelerating.

Which of the following statements is true, according to Kepler's third law?

The larger the orbit, the longer it takes for the planet to complete one revolution.

Why were Newton's three laws so important to astronomy?

They showed that planets can move around the Sun by themselves forever, without coming to rest

If you were observing Earth's motion from another planet, would you observe occasional retrograde motion?

Yes, from any of the planets.

A distant asteroid is discovered that takes 50 years to orbit once around the Sun. According to Kepler's third law, what is the average distance of this asteroid from the Sun?

13.6 AU (cube root of 2500)

Kepler's second law states that a line joining a planet to the Sun

sweeps out equal areas in equal times.