Question 1

An astronaut is piloting a spacecraft, which is in a circular orbit around Earth. A space station is ahead, on the same circular orbit. If he fires his rockets briefly to decrease the forward speed of the rocket, what will happen?

Accepted Answer

The spacecraft will be put into an elliptical orbit with an apogee equal to the original radius.The average radius of this orbit is smaller,so it will take less time to complete one revolution.So if the speed increment is calculated correctly,when he completes one revolution,bringing him back to the original radius,he could be caught up with the station.At that point,a forward burst could put him in the same circular orbit as the station.

Question 2

State Kepler's First Law of Orbital Motion

Accepted Answer

The orbits of the planets are ellipses,with the Sun at one focus.

Question 3

Our Moon revolves about Earth in the same direction as Earth's direction of rotation about its own axis. The gravitational attraction of the Moon causes tides on Earth, which gradually slow down its rotation about its own axis. What consequences does this have for the Moon?

Accepted Answer

Since the angular momentum of the Earth-Moon system has to be conserved,a decrease in the angular momentum of Earth about its axis must be balanced by an increase of the Moon's angular momentum about that axis.The radius of the Moon's orbit will thus gradually increase until it escapes from the gravitational field of Earth.

Question 4

There are daily variations in the barometric pressure, which occur because of tidal effects.

Accepted Answer

Tidal effects can cause daily variations in barometric pressure.

Question 5

Why are planets and stars approximately spherical, whereas asteroids and meteorites are shaped like ordinary rocks?

Accepted Answer

The answer of Why are planets and stars approximately spherical,...

Question 6

Triton, the largest of Neptune's moons has a retrograde rotation. This means that it revolves about Neptune in the opposite direction to Neptune's direction of rotation about its own axis. The gravitational attraction of Triton causes tides on Neptune, which gradually slow down its rotation about its own axis. What consequences does this have for Triton?

Accepted Answer

The answer of Triton, the largest of Neptune's moons has...

Question 7

A star is in an elliptical orbit around a black hole (which can't be seen). You have been observing the motion of the star through a telescope and have followed the motion long enough to establish that it is elliptical. How can you determine on which focus of the ellipse the black hole is located?

Accepted Answer

The answer of A star is in an elliptical orbit...

Question 8

For a satellite in orbit around Earth, the product of its speed times the distance from the center of Earth has the same value when the satellite is at the perigee, its closest approach to Earth, and at the apogee, its furthest point from Earth. Is the product the same at other points on the orbit?
 Why?

Accepted Answer

The answer of For a satellite in orbit around Earth,...

Question 9

The gravitational force that the Sun exerts on Earth is much larger than the gravitational force that Earth exerts on the Sun.

Accepted Answer

According to Newton's third law of motion, the gravitational force between two objects is always equal in magnitude but opposite in direction. Therefore, the gravitational force that Earth exerts on the Sun is equal in magnitude to the gravitational force that the Sun exerts on Earth.

Question 10

A mass is attached to a fixed point by means of an ideal spring with zero unstretched length and is free to move in two dimensions. What would be the equivalent statement of Kepler's third law for this situation in the case of circular orbits around the fixed point?

Accepted Answer

The answer of A mass is attached to a fixed...

Question 11

State Kepler's Third Law of Orbital Motion

Accepted Answer

The answer of State Kepler's Third Law of Orbital Motion...

Question 12

The reason that when an object falls towards Earth, Earth does not move toward the object, is that the force exerted by Earth on the object is so much bigger.

Accepted Answer

The force exerted by Earth on the object and the force exerted by the object on Earth are equal in magnitude and opposite in direction, according to Newton's third law of motion. However, Earth's much larger mass results in an imperceptible acceleration compared to the object.

Question 13

Tidal locking is what makes the Moon rotate about its own axis at the same rate that it revolves around Earth. Using as a model of a moon two identical masses of mass m connected by a light rod, explain how the forces on the masses would tend to keep this satellite in a fixed orientation.

Accepted Answer

The answer of Tidal locking is what makes the Moon...

Question 14

A binary system has two stars of mass M circling their common center of mass on opposite sides of a circle of radius R. What is the potential energy of the system?

Accepted Answer

The answer of A binary system has two stars of...

Question 15

Four identical bodies of mass M, at the vertices of a square with a diagonal 2R, orbit their common center of mass in a circular motion with a radius R. How much energy is required to separate the four stars so they are an infinite distance apart?

Accepted Answer

The answer of Four identical bodies of mass M, at...

Question 16

The Schwarzchild radius is defined for a given mass M as the radius for which the escape velocity would be exactly equal to the speed of light, c. What is the expression for this radius in terms of G, M, and c?

Accepted Answer

The answer of The Schwarzchild radius is defined for a...

Question 17

An astronaut is piloting a spacecraft, which is in a circular orbit around Earth. A space station is ahead, on the same circular orbit. If he fires his rockets briefly to increase the forward speed of the rocket, what will happen?

Accepted Answer

The answer of An astronaut is piloting a spacecraft, which...

Question 18

The ground rises and sinks regularly because of tidal effects.

Accepted Answer

Tidal forces from the moon and sun cause the Earth's oceans to rise and fall in a regular pattern, known as tides. This effect can also cause the ground to rise and sink slightly, but only in areas near the coast where the land is influenced by the tides.

Question 19

Tides are approximately 24 hours apart.

Accepted Answer

Tides occur approximately every 12 hours and 25 minutes, not 24 hours. This is because they are influenced by the rotation of the Earth and the gravitational pull of the moon and sun.

Question 20

State Kepler's Second Law of Orbital Motion

Accepted Answer

The answer of State Kepler's Second Law of Orbital Motion...

Quiz 12: Gravity