Gravitational and electric fields

Question 1

In what way is T (period) related to r (orbital radius)?

Answer 1

T ² ∝ r ³

Question 2

What is the equation for escape velocity?

Answer 2

v = √((2GM)/r)

Question 3

What is gravitational potential energy?

Answer 3

The energy required to bring unit mass (1kg) from infinity to that point.

Question 4

If the force between two charged objects in an electric field is attractive, is the force positive or negative?

Answer 4

Negative

Question 5

If the force between two charged objects in an electric field is repulsive is the force positive or negative?

Answer 5

Positive

Question 6

What is the meaning of E in terms of electric fields?

Answer 6

Electric field strength.

Question 7

If a positivity charged particle is moving through an electric field, which direction will the force act in?

Answer 7

The same direction as the electric field lines.

Question 8

If a negatively charged particle is moving through an electric field, which direction will the force act in?

Answer 8

The opposite direction to the electric field lines.

Question 9

In terms of electric fields, what does V mean and what is the unit?

Answer 9

Absolute electric potential, Volt (V).

Question 10

How would you draw a gravitational field around and object?

Answer 10

Vector lines pointing into the object from many directions which are equally spaced apart.

Question 11

What is the relationship of the law of gravitation?

Answer 11

Follows the inverse square law: F ∝ 1/r²

Question 12

If the distance between masses doubles, what will be the strength of the force of gravitation?

Answer 12

One quarter of the strength of the original force.

Question 13

What is the unit of gravitational field strength, g?

Answer 13

N/kg (m/s²)

Question 14

Is g a vector or a scalar?

Answer 14

A vector.

Question 15

What is the shape of a gravitational field?

Answer 15

Radial.

Question 16

What is gravitational potential?

Answer 16

The gravitational potential energy that a unit mass would have at a point.

Question 17

What is the sign of gravitational potential and gravitational potential energy?

Answer 17

Negative.

Question 18

What happens to the gravitational potential and gravitational potential energy as the distance from the body increases?

Answer 18

They become less negative.

Question 19

What is the gravitational potential and gravitational potential energy at infinite distance from the body?

Answer 19

Zero.

Question 20

what does the area under a gravitational field strength against distance graph give?

Answer 20

Change in gravitational potential.

Question 21

What is gravitational potential difference?

Answer 21

The energy needed to move a unit mass.

Question 22

When is work done in a gravitational field?

Answer 22

When moving against the force of gravity; when changing equipotentials.

Question 23

How is the speed of a satellite related to its orbital radius?

Answer 23

The speed is inversely proportional to the square root of its orbital radius;
v ∝ 1/√r

Question 24

How do you calculate the total energy of a satellite?

Answer 24

Kinetic energy + potential energy.

Question 25

How does the total energy of a satellite vary?

Answer 25

It doesn’t, total energy is always constant.

Question 26

How does the speed of a satellite change as it travels around an elliptical orbit?

Answer 26

It will speed up as its height decreases and vice versa.

Question 27

What are geostationary satellites useful for?

Answer 27

Sending TV and telephone signals as you don’t need to alter the angle of your receiver or transmitter to keep up.

Question 28

How high are low orbiting satellites?

Answer 28

Between 180-2000km above the Earth’s surface.

Question 29

What are low orbiting satellites useful for?

Answer 29

Imaging, spying, monitoring the weather and communications although multiple satellites will be needed to maintain constant coverage.

Question 30

Which parts of the Earth do low orbiting satellites cover?

Answer 30

All of it over multiple orbits.

Question 31

Where must geostationary satellites be over the Earth in order to maintain their orbit?

Answer 31

Directly above the equator.