Gravitational and electric fields

Question 1

Newtons law of gravitation

Answer 1

F = Gmm/r^2

Question 2

Escape velocity

Answer 2

v = √2GM/r

Question 3

Orbital speed

Answer 3

mv^2/r = GMm/r^2

v^2 = GM/r

v = √GM/r

v ∝ 1/ √r

Question 4

Time for satellite to orbit

Answer 4

v = 2πr/T

T = 2πr/v

T = 2πr/ (√GM/r)

T = 2πr√r/√GM

T = √4π^2r^3/GM

T^2 ∝ r^3 or T ∝ √r^3

Question 5

Gravitational potential at a point

Answer 5

The energy required in bringing 1 unit mass from infinity to the point

Question 6

What is a force field

Answer 6

A region in which a body experiences a non-contact force

Question 7

Why is there a negative sign in the equation used for calculating gravitational potential

Answer 7

Gravitational potential is negative on the surface and increases with distance from the mass. It is negative because it is the work that has to be done against the field

Question 8

the gradient of V against r gives you

Answer 8

g

Question 9

the area under the graph of g against r

Answer 9

gravitational potential difference

Question 10

What is gravitational potential difference

Answer 10

The energy needed to move a unit mass between two points

Question 11

Kinetic and potential energy of satellites

Answer 11

The total energy (Ke and Pe) is always constant

Question 12

What is the escape velocity

Answer 12

The minimum speed an unpowered object needs to escape a gravitational field

Question 13

applications of geostationary and low orbiting satellites

Answer 13

Geostationary means it travels at the same angular speed as the Earth: Good for TV and phone signals

Low orbit is anything between 180 and 2000km above Earth: Used for imaging and monitoring the weather

Question 14

When a charged particle enters an electric field at right angles

Answer 14

It follows a parabolic trajectory