Gravitational Fields

Question 1

How is the force between two objects calculated?

Answer 1

F = (-G)M1M2/r^2

Question 2

How is gravitational field strength calculated?

Answer 2

g = -GM/r^2

Question 3

What is the unit of gravitational field strength?

Answer 3

N/kg

Question 4

How is gravitational field potential calculated?

Answer 4

Vg= -GM/r

Question 5

How is gravitational potential energy calculated?

Answer 5

GPE = mVg = -GMm/r

Question 6

What is the mass of the Earth?

Answer 6

6 x 10^24kg

Question 7

What is the radius of the Earth?

Answer 7

6370km

Question 8

What is the main property of the gravitational field lines around a spherical mass?

Answer 8

They are radial

Question 9

What is the escape velocity of an object?

Answer 9

The minimum speed an object without propulsion needs to be able to escape from the gravitational field of a mass.

Question 10

How is the gravitational force on a satellite calculated?

Answer 10

Fg = -GMem/r^2

Question 11

How is centripetal force calculated?

Answer 11

Fc = -mv^2/r

Question 12

How is the speed needed for a satellite to stay in orbit calculated?

Answer 12

v = √(GMe/re + h)

Question 13

How is the time period of an orbit calculated?

Answer 13

T = 2πr/v

Question 14

What is the relationship between time period and orbital radius?

Answer 14

T^2 ∝ r^3

Question 15

How is the time period of an orbit calculated using the radius of the orbit?

Answer 15

T^2 = (4π^2/GMs)r^3

Question 16

How is the gravitational potential at a point defined?

Answer 16

The work done in moving a 1kg mass from infinity to that point.

Question 17

What is the total energy of a satellite?

Answer 17

GPE + KE = -GMems/2R

Question 18

How is the work done needed to move an object from a point at distance R from Earth’s centre to infinity?

Answer 18

GMems/R