Out into space

Question 1

Describe the acceleration of an object moving in a circle

Answer 1

Constantly accelerating towards the centre

Question 2

What is centripetal force?

Answer 2

The force which causes the acceleration towards the centre and keeps an object in circular motion

Question 3

What direction is the centripetal force acting?

Answer 3

Always at right angles to the motion of the object

Question 4

What is angular frequency?

Answer 4

measure of the rate of rotation of an object

Question 5

How do you define the angle in radians?

Answer 5

The arc-length divided by the radius

Question 6

How do you define angular velocity and what are the units?

Answer 6

ω = θ/t rads-1

angle/time

Question 7

How is linear velocity and angular velocity related?

Answer 7

v = rω

r is the radius o the circle

Question 8

What is frequency in terms of circular motion?

Answer 8

The no. of complete revolutions per second

Question 9

What is the period in terms of circular motion?

Answer 9

The time taken for a complete revolution

Question 10

How is angular velocity related to frequency and time?

Answer 10

ω = 2πf

ω = 2π / T

Question 11

Why is an object moving with constant speed in a circular motion accelerating?

Answer 11

Acceleration is the rate of change of velocity and as the direction is constantly changing the velocity is changing

Question 12

Whats acceleration directed towards the centre of a circle called?

Answer 12

centripetal acceleration

Question 13

What is the equation for centripetal force and how is it derived?

Answer 13

F = mv2 / r

F = mω2 r

Comes from F=ma as a=v2/r or a=ω2r

Question 14

What would happen to an object if the centripetal force was removed?

Answer 14

Would fly off at a tangent

Question 15

What are the equation for centripetal acceleration?

Answer 15

a = v2 /r

a = ω2 r

Question 16

What do masses in a gravitational field experience?

Answer 16

A force of attraction

Question 17

What is Newton’s Law of Gravitation?

Answer 17

All particles with mass attract all other particles by a force called gravitation

Question 18

Why is there a minus sign when calculating gravitational force?

Answer 18

Shows the force is attractive

Question 19

What is a gravitational field?

Answer 19

A region where an object will experience a non-contact force

Question 20

What is a uniform field?

Answer 20

A field that is the same everywhere

Question 21

What is a point mass?

Answer 21

An object who’s mass is concentrated at their centre

Question 22

What type of field do point masses have?

Answer 22

radial field

Question 23

When close to the Earth’s surface why can you assume that the field is perfectly uniform?

Answer 23

The field lines are almost parallel and are evenly spaced

Question 24

What is the equation that shows Newton’s law of gravitation?

Answer 24

F = GmM / r^2

Question 25

What is gravitational field strength?

Answer 25

Force per unit mass

Question 26

What does gravitational field strength depend on?

Answer 26

Where you are in a field

Question 27

What is the equation for finding gravitational field strength?

Answer 27

g = Fgrav / m

( Fgrav = GmM / r2 so gravitational field strength is GM/r2 )

Question 28

Is gravitational field strength a vector?

Answer 28

Yes it has direction - towards the centre of mass

Question 29

What is another way to describe the gravitational field strength?

Answer 29

Acceleration due to gravity

Question 30

What is the principle of the conservation of energy?

Answer 30

Energy cannot be created to destroyed, it can only be transferred from one form to another

Question 31

What is gravitational potential energy?

Answer 31

The work done on an object when bringing it from infinity to a given point

Question 32

What is the equation for gravitational potential energy?

Answer 32

Egrav = - GMm / r

Question 33

What is the potential energy at infinity?

Answer 33

zero

Question 34

Why does a mass gain potential energy when you move it away from Earth?

Answer 34

Because potential energy is negative so as you move it away it gains potential energy as at infinity potential energy is zero

Question 35

What does the gradient at a given point show on a gravitational potential energy - r graph?

Answer 35

Gravitational force (gradient is steepest when distance is smallest as it is closer to the centre of mass so field lines closer together)

Question 36

Why does the potential energy of a mass change as you move it between two different distances?

Answer 36

Work is done against the force of gravity (or work is done by the force of gravity)

Question 37

What does the area under a Fgrav - r graph represent?

Answer 37

Gravitational potential energy

Question 38

What is gravitational potential?

Answer 38

Potential energy per unit mass

The work done on an object per unit mass in bringing it from infinity to a given point

Question 39

What is the equation for gravitational potential?

Answer 39

Vgrav = - GM / r

Question 40

What does the gradient of a Vgrav - r graph represent?

Answer 40

Gravitational field strength, g

Question 41

What does the area under a gravitational field strength (g) - r graph represent?

Answer 41

Gravitational potential (Vgrav)

Question 42

What do equipotentials show?

Answer 42

The points in a field which all have the same field strength

Question 43

What happens when you travel along a line of equipotential?

Answer 43

You don’t lose or gain energy (no work is done against gravity)

Question 44

What is perpendicular to equipotentials?

Answer 44

Field lines

Question 45

What is a satellite?

Answer 45

Any smaller mass that orbits a much larger mass

Question 46

How do you find the velocity of a satellite? (what two equations do you equate)

Answer 46

centripetal force = mv2 / r
gravitational force = GmM / r2

∴ v = √(GM/r)

Question 47

How can a mass ‘esacape’ the gravitational ‘well’ of a planet?

Answer 47

KE ≥ GPE

Question 48

How do you derive the escape velocity?

Answer 48

KE ≥ GPE

1/2 mv2 ≥ GMm / r2

∴ escape velocity = √(2GM/r)