Module 5.4 - Gravitational Fields

Question 1

Define a gravitational field

Answer 1

The region around a body in which other bodies will feel a force due to the mass of the body

Question 2

Define the gravitational field strength (at a point in the field)

Answer 2

The force acting per unit mass at that point

Question 3

State Newton’s law of gravitation

Answer 3

The gravitational force of attraction between two point masses is directly proportional to the product of their masses and inversely proportional to the square of their separation

Question 4

What are Kepler’s laws of planetary motion?

Answer 4

Planets travel around the Sun in elliptical orbits
A line joining the Sun to a planet will sweep out equal areas in equal times
The time period of the orbit squared is proportional to the mean radius of the orbit cubed

Question 5

Define geostationary orbit

Answer 5

An orbit of the Earth made by a satellite that has the same time period and orbital direction as the rotation of the Earth and is in the equatorial plane

Question 6

Uses of geostationary satellites

Answer 6

Broadcasting TV signals
Relaying phone signals
Monitoring the weather
Monitoring air traffic

Question 7

Define gravitational potential (at a point in a gravitational field)

Answer 7

Work done in moving unit mass from infinity (where the gravitational potential is 0) to that point

Question 8

Difference between gravitational potential and gravitational potential energy

Answer 8

Gravitational potential measures the work done moving mass towards the body
Gravitational potential energy measures the work done moving mass away from the body

Question 9

Define escape velocity

Answer 9

Minimum launch velocity required to move an object from that point to infinity