Grav Fields P2

Question 1

What is the magnitude of the gravitational force of two objects proportional to?

Answer 1

The mass of both objects

Question 2

What is the magnitude of the gravitational force of two objects inversely proportional to?

Answer 2

The distance from the centre of both objects squared (Inverse square law)

Question 3

What is a point mass?

Answer 3

Where the mass is concentrated at a single point

Question 4

What is gravitational field strength?

Answer 4

The gravitational force per unit mass of a test mass

Question 5

What is a test mass?

Answer 5

A particle with a very small mass used to test a gravitiational field without affecting it

Question 6

What is gravitational potential energy?

Answer 6

The amount of energy/work done required to move a mass from infinity to a given point in a gravitational field

Question 7

What is gravitational potential energy at infinity?

Answer 7

Zero

Question 8

What happens to the GPE as it gets closer to the source mass?

Answer 8

The more negative the GPE becomes

Question 9

What is escape velocity?

Answer 9

The minimum velocity required for an object to move from a point in a planet’s gravitational field to a point where the gravitational field is negligible.

Question 10

What is gravitational potential?

Answer 10

The work done to move a 1kg mass from infinity to a point in the field

Question 11

What are equipotentials?

Answer 11

A set of points which have the same gravitational potential

Question 12

What is potential gradient?

Answer 12

The change in potential per unit distance at that point.

Question 13

What does the area between two points below a gravitational field strength graph tell us?

Answer 13

The gravitational potential difference

Question 14

At what seperations are equipotentials when the gravitational field strength is high?

Answer 14

Large seperations

Question 15

What do satellites do in low Earth orbits?

Answer 15

They move over lots of different points on the surface and orbit relatively close to the surface

Question 16

What do satellites do in geostationary orbits?

Answer 16

They appear to stay still in the sky over a single point on the surface and orbit at distances relatively far from the surface

Question 17

How do you derive the escape velocity?

Answer 17

Set the equations of kinetic energy and gravitational force equal to each other

Question 18

What is the formula for the total energy of a satellite?

Answer 18

-GMm/2r

Question 19

Why is gravitational potential difference a negative value?

Answer 19

Because work needs to be done to move an object from the inside of the field to the outside. Since infinity is zero, below infinity must be negative

Question 20

How is the orbital period realted to the radius of a circular orbit?

Answer 20

T^2 = k x r^3

Question 21

How could you find the speed of an orbiting satellite?

Answer 21

Set the centripetal force to the gravitational force and sub in v=2πr/T