Astrophysics

Question 1

What are Kepler’s 3 Laws ?

Answer 1

1. The planets Move in elliptical orbits with the sun at one of the two foci. ( foci is centre of interest/activity)
2. The radius vector drawn from the sun to a planet sweeps out equal area in equal time.
3. The Square of the orbital period is proportional to the cube of the semi-major axis ( T^2 is proportional to r^3).

Question 2

A satellite in orbit will have what two types of energy?

Answer 2

Kinetic and Gravitational Potential energy

Question 3

By Convention, how is gravitational potential energy defined?

Answer 3

It is defined as 0 joules at Infinity

Question 4

Ep=mgh can only be used if what?

Answer 4

the value of ‘g’ is constant, which only works over small ranges.

Question 5

Gravitational fields are what types of fields?

Answer 5

Conservative fields

Question 6

Explain a Conservative Field

Answer 6

In a conservative field any round trip (start and end at same point) requires no work to be done. If no work is done then energy is conserved.

Question 7

what can you think of a gravitational potential well as?

Answer 7

A three dimensional funnel

Question 8

How does a gravitational potential well explain why a satellite remains in orbit?

Answer 8

It can be thought of as a 3D funnel with the satellite moving at a set height in a fixed path. Gravitational field is a conservative field so there is no loss of energy. therefore the satellite will remain in a stable circular orbit indefinetely.

Question 9

What would happen to a satellite in a non-conservative field?

Answer 9

a mass follows a decaying orbit around the centre, as friction causes the mass to lose Kinetic Energy. This continues until the mass falls into the central hole.

Question 10

Each planet has its own unique atmospheric composition. Why?

Answer 10

Atmospheric gases are bound to a planet due to gravity, to escape a planet they must reach escape velocity.

Question 11

the lighter the element the more likely it is to reach escape velocity. Why?

Answer 11

the lighter the element, the higher the average velocity of the molecules withing the gas.

Question 12

Why can the gas giants retain much lighter molecules than earth?

Answer 12

The larger the planet the higher the escape velocity.

Question 13

Describe thermal escape of atmospheric gases?

Answer 13

Thermal escape is when the molecular velocity is sufficiently high due to thermal energy.( particularly in the exosphere of the Earth) Mercury has no atmosphere due to the fact it has a hot atmosphere with higher molecular velocities and therefore a greater chance of escape.