Gravitational Fields

Question 1

Define Gravitational Field

Answer 1

A region where an object that has mass, experiences a force

Question 2

State newton’s law of gravitation and state equation it comes from

Answer 2

Attractive forces between two point masses is directly proportional to the product of their masses and inversely proportional to the square of their seperation
F=GMm/r^2

Question 3

Define Gravitational Field strength and state the equation it comes from

Answer 3

Force acting on a body per unit mass
G=F/m

Question 4

Equations for potential energy for uniform and radial field and define potential energy

Answer 4

Uniform, Ep=mgh
Radial = (Gm1m2)/r
Work done in moving object with mass from infinity to that point in the field

Question 5

Define absolute Gravitational potential energy

Answer 5

Work done per unit mass in moving a body from infinity to that point in Gravitational Field
V=GM/r
Work done = m x V

Question 6

Derive two equations to show Kepler’s 3rd Law

Answer 6

Question 7

Derive two equations for equation of orbital velocity

Answer 7

Question 8

Derive two equations to get equation for escape velocity

Answer 8

Question 9

Derive two equations for total orbital energy

Answer 9

Question 10

State times for Low earth orbit (LEO), Medium earth orbit (MEO), High earth orbit (HEO)

Answer 10

LEO : less than 2 hours
MEO : More than 2 hours and less than 24 hours
HEO : greater than 24 hours

Question 11

Similarity and difference between geostationary and geoschrynous orbits, state advantage of geostationary

Answer 11

Similarity : time period of 24 hours
Differnce : geostationary orbits above same point Earth’s equator
Geoschrynous orbit do not stay above same points of Earth’s surface
Advantage : easier to track

Question 12

State uses of geostationary orbits
State a little explanation

Answer 12

Monitoring weather : whole earth may be scanned
GPS : several satellites needed to fix position on earth
Communications : limited by intermittent contact

Question 13

Problem of putting more satellites in orbit

Answer 13

Satellites orbit in closer proximity
Greater risk of collisions

Question 14

What is meant by satellites in polar orbits
State uses

Answer 14

Satelite passes over north and south poles
Making them ideal for espionage (spying on other countries)

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Question 21

Answer 21

A

Question 22

Answer 22

Speed = distance / time
Distance = 2.04 x 10^7
Can’t use Kepler’s third law as that gives the orbital of the earth, so your radius would just be equal to radius of earth

Question 23

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Question 25

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D

Question 26

Answer 26

A

Question 27

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Question 28

which one has different units to the other 3 a) gravitational potential b) gravitational field strength c) force per unit mass d) gravitational potetnial gradient

Answer 28

Question 29

State what is meant by terminal velocity

Answer 29

Minimum speed at the Earth's surface that will allow an object to leave

Question 30

State two reasons why a rocket does not need the escape velocity to leave the Earth's surface

Answer 30

- they aren't given all their Kinetic energy at the Earth's surface as energy is continually added in the flight - less energy needed to achieve orbit than to escape from Earth's gravitational field

Question 31

Explain why all potential energy values are negative

Answer 31

Zero potential at infinity Energy input needed to move to infinity Work done by Field moving object from infinity

Question 32

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Question 33

Explain how change in potential energy relates to kinetic energy when satellites orbit alters

Answer 33

Loss of gpe is twice gain in kenetic energy

Question 34

Skip first part calculating force

Answer 34

Question 35

Explain why astronauts in an orbiting space vehicle experience the sensation of weightlessness

Answer 35

Both astronaut and vehicle are traveling at the same orbital speed They have the same centripetal acceleration / they are in freefall No normal reaction between astronaut and vehicle

Question 36

Explain what is meant by Gravitational potential in at a point in Gravitational Field

Answer 36

Work done against the field per unit mass When moved from infinity to the point

Question 37

-63 equals gravitational potential at the surface of the earth

Answer 37

Question 38

State two features of a geo-sychronous orbit

Answer 38

Period is 24 hours Remains in fixed position relative to surface of earth Same angular speed as earth Equatorial orbit

Question 39

Answer 39

Signal would be to weak at a large distance Signal spreads out more further it travels making detection and transmission and less effective

Question 40

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Question 41

If you have been asked to calculate the gravitational force between two objects and they say calculate the force when the seperation changes, what must you remember to do and not do

Answer 41

Question 42

Answer 42

D

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Question 44

State what is represented by Gravitational field lines

Answer 44

Direction and magnitude of force on mass placed in the force field

Question 45

Answer 45

Lines are closer together so field is stronger Material forming the Earth at K has a higher density than the surrounding material

Question 46

Only 6.3

Answer 46

Ball will speed up / accelerates when moving towards K because potential at K is lower

Question 47

In a gravitational field should lines point away or towards object

Answer 47

Towards object, if a ay then it is not a gravitational field

Question 48

Only 6.6

Answer 48

Should be at right angles and sop and bottom should be symmetrical

Question 49

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Question 52

The Moonís orbit around the Earth may be assumed to be circular. Explain why no work is done by the gravitational force that acts on the Moon to keep it in orbit around the Earth.

Answer 52

work = force × distance moved in direction of force (in circular motion) force is perpendicular to displacement no movement in direction of force hence no work

Question 53

Define Gravitational potential difference

Answer 53

The energy needed to move a unit mass between two points in a Gravitational Field

Question 54

What is an equipotential surface

Answer 54

A surface in which the potential is constant at every point

Question 55

How are equipotential surfaces found

Answer 55

Through joining points off equal potential together to map out a surface

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