Gravitation

Question 1

Define Newtons law of Gravitation

Answer 1

The force of attraction between two point masses is proportional to the product of the two masses and are inversely proportional to the square of the distance between them

Question 2

Define the gravitational potential at a point in a gravitational field

Answer 2

Gravitational potential at a point, is defined as the energy required to move a unit mass from infinity to that point

Question 3

Define escape velocity

Answer 3

The minimum velocity an object must have at the surface of a planet to escape the pull of gravity, using its own kinetic energy.

Question 4

What is the units of gravitational potential

Answer 4

Jkg^-1

Question 5

What is the units of G (Gravitational Constant)

Answer 5

NM^2kg^-2

Question 6

What is a gravitational field

Answer 6

A region in space in which a massive object experiences a gravitational force

Question 7

What are the units for gravitational field strength

Answer 7

Nkg^-1

Question 8

How does an object lose potential energy when at infinity

Answer 8

An object has no joules of energy when it has been moved an infinite distance from the planet

An object that moves from this point of infinity, back to the planet loses potential energy

Question 9

Define gravitational field strength

Answer 9

Force per unit mass that the field strength has at that point

Question 10

What is the unit for gravitational force

Answer 10

Newtons

Question 11

What are the advantages of a geo-synchronous orbital satellite

Answer 11

maintains a fixed position relative to surface of Earth (1)
period is 24 hrs (1 day) or same as for Earth’s rotation (1)
offers uninterrupted communication between transmitter and receiver (

Question 12

Define gravitational potential

Answer 12

Gravitational potential is the potential energy per kilogram at a point in a field.

Question 13

What is fundamental about gravitational fields

Answer 13

• Always attractive

Question 14

Why do rockets not need to have an escape velocity for Earth to reach orbit?

Answer 14

-They are not going to infinity, just escaping a gravitational field
- Does not rely on kinetic energy, relies on chemical
energy produced by thrusters

Question 15

Define coulombs law

Answer 15

The force between two charges is proportional to the product of the charges and proportional to 1 over the square of the distance between them

Question 16

Is an Electric field a vector or scalar quantity

Answer 16

vector - it has both magnitude and direction

Question 17

Explain the path of a charge in a electrical field

Answer 17

The path is a parabola. As the electron is negatively charged, it experiences a constant acceleration upwards due to the horizontal field. Its horizontal velocity remains constant but its vertical velocity is constantly changing

Question 18

Define absolute electric potential

Answer 18

The potential difference between a point and a point at zero potential, which is infinitely far away

Question 19

Define potential difference

Answer 19

The work done against an electric field, in moving unit charge from one point to a second point at a higher potential. If charge moves from a point of higher potential to lower potential work is done by the electric field.

Question 20

If a charge is negative, explain how it would reach infinity

Answer 20

In this case, the charge is negative, work must be done against the field in order to reach infinity. Therefore the charge gains Ep as it moves to infinity. This is because at infinity the potential energy is zero. So the potential in the field must be negative.

Question 21

What is fundamental about an electric field

Answer 21

Always positive, regardless of position

Question 22

What is the units for electric field strength

Answer 22

Vm^-1

Question 23

Why is gravitational potential always negative

Answer 23

• At infinity, gravitational potential is zero
• This means the potential near to any planet is a
  negative quantity, because potential energy decreases
  as something falls towards the planet

Question 24

What is the equation for gravitational potential energy

Answer 24

Ep = ∆V x m

Question 25

Electric potential at a point

Answer 25

electric potential at a point is defined as the amount of work done in moving a unit positive charge from infinity to that point.

Question 26

Field

Answer 26

area of space where mass/charge experience a force

Question 27

field lines

Answer 27

show the direction of the force on a point mass/positive test charge

Question 28

What is the K constant for the electric field equation

Answer 28

K= 9x10^9

Question 29

Field strength

Answer 29

How much force something would feel

Question 30

Definition of potential

Answer 30

Energy needed to move 1kg of mass or 1 coulomb of charge to move from infinity to that point