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OCR Physics B Unit 4 > 4.2 Out Into Space > Flashcards

4.2 Out Into Space Flashcards

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1
Q

What is a vector quantity?

A

Something that has magnitude and direction.

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2
Q

Give the equation for momentum.

A

p = m v

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3
Q

What the the units of momentum?

A

kg m s^-1 (or Ns)

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4
Q

Is momentum always conserved?

A

Yes.

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5
Q

What is Newton’s 1st law of motion?

A

The velocity of an object will not change unless a resultant for acts upon it.

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6
Q

What is the resultant force on an object moving at a constant speed?

A

Zero

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7
Q

What is Newton’s 2nd law of motion?

A

The rate of change of momentum of an object is directly proportional to the results force which acts upon the object.

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8
Q

Give the equation for Newton’s 2nd law.

A

F = ∆mv / ∆t

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9
Q

Give the equation for Newton’s 2nd law for when mass does not change.

A

F = ma

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10
Q

What is the resultant force?

A

The vector sum of all forces acting on an object.

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11
Q

What are the units for force?

A

Newtons, N.

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12
Q

What are the units for mass?

A

Kilograms, kg.

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13
Q

If which direction will acceleration occur if there is a resultant force?

A

In the direction of the resultant force.

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14
Q

What is Newton’s 3rd law?

A

If object A exerts a force on object B, then object B exerts an equal but opposite force on object A.

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15
Q

Gravity pulls down on a book whilst a table pushes upward on the book. Why is this not a case of Newton’s 3rd law?

A

Because the forces are not of the same type. Gravity pulling the Earth up would be an example of Newton’s 3rd law though.

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16
Q

Work is done when…

A

Energy is transferred.

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17
Q

Give the equation for work done.

A

Foce x Distance

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18
Q

What are the units for work done?

A

Joules, J.

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19
Q

How could you find work done from a graph?

A

Find the area under a F vs s graph.

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20
Q

W = F s cosθ where θ is…

A

The angle between the force and the direction of motion.

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21
Q

Energy cannot be created or destroyed but it can be…

A

Transferred from one form to another.

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22
Q

Give the equation for efficiency.

A

Efficiency = useful power output / total power output

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23
Q

Name three types of potential energy.

A

Gravitational, elastic and electrical.

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24
Q

Give the equation for gravitational potential energy of objects moving close to the Earth’s surface.

A

E = m g ∆h

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25
Q

Define radians.

A

The arc-length divided by the radius of the circle.

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26
Q

How many radians are in a complete circle?

A

2π.

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27
Q

Convert 45º into radians.

A

π/4 rad.

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28
Q

What is the definition of angular speed?

A

The angle an object rotates though per second.

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29
Q

Give the equation for angular speed, ω.

A

ω = θ / t

30
Q

Give the equation for linear speed in terms on angular speed.

A

v = r ω

31
Q

What is the equation for frequency in terms of time period?

A

f = 1 / T

32
Q

Give the angular speed of an object in terms of frequency (in revolutions per second).

A

ω = 2 π f

33
Q

A car is travelling at a constant speed in a circular motion. Why is it accelerating?

A

It’s velocity is changing since it’s direction is changing and acceleration is rate of change of velocity.

34
Q

Give an equation for radial acceleration in terms of linear speed.

A

a = v^2 / r

35
Q

Give an equation for centripetal acceleration in terms of angular speed.

A

a = ω^2 r

36
Q

Give an equation for radial acceleration in terms of angular speed and linear speed.

A

a = v ω

37
Q

Give two equations for centripetal force.

A 
F = mv^2 / r
F = m ω^2 r
38
Q

Any mass in a gravitational field will experience an…

A

Attractive force.

39
Q

Force experienced in a gravitational field is always…

A

Attractive, never repulsive.

40
Q

Gravitational force experience depends on what?

A

The masses of the two objects and the distance between them.

41
Q

What is a point mass?

A

Objects that behave as if all their mass is acting at a single point.

42
Q

What is Newton’s law of gravitation?

A

F = -(G M m) / r^2

43
Q

What does r represent in Newton’s law of gravitation?

A

The distance between the centre of the two masses.

44
Q

What is G in Newton’s law of gravitation, and what is it’s value?

A

The gravitational constant. 6.67 x 10^-11

45
Q

What are gravitational lines of force (field lines)?

A

Lines with arrows that show the direction of the force that masses would feel in a gravitational field.

46
Q

If you double the distance between two objects, the gravitational force experienced by the objects will…

A

Be one quarter of the original value.

47
Q

Descrive a radial field.

A

A field where the field lines meet at the centre of a mass..

48
Q

What is a uniform field and where might you find one?

A

A field where the field lines are parallel. At the Earth’s surface.

49
Q

What is field strength, g, defined as?

A

Force per unit mass.

50
Q

What are the units of field strength?

A

N kg^-1

51
Q

g is a vector quantity. Where does the vector point?

A

To the centre of the mass of the field being described.

52
Q

Why do you assume g is constant around the surface of the Earth?

A

Because the field at the surface of the Earth is almost uniform.

53
Q

What is the value of g (acceleration due to gravity) at the Earth’s surface?

A

-9.81 m s^-2 (N kg^-1)

54
Q

What is the gravitational force experienced by an object in a uniform field?

A

mg

55
Q

The force experienced by a mass in a uniform field is?

A

Constant.

56
Q

In a uniform gravitational field, potential energy increases with…

A

Height.

57
Q

What is the equation for change in gravitational potential energy in a uniform gravitational field?

A

∆PE = m g ∆h

58
Q

In a radial field, g is inversely proportional to…

A

r^2

59
Q

Give the equation for field strength in a radial field.

A

g = -(G M) / r^2

60
Q

In a radial field, you gain gravitational potential energy if you move away from…

A

The mass causing the field.

61
Q

Give the equation for gravitational potential energy in a radial field.

A

E grav = - (G M m) / r

62
Q

Where is potential energy defined as zero?

A

At an infinite distance away from the mass.

63
Q

Is gravitational potential energy at the Earth’s surface positive or negative?

A

Negative.

64
Q

What is gravitational potential defined as?

A

The gravitational potential energy per unit mass.

65
Q

What are the units of gravitational potential?

A

J Kg^-1

66
Q

What is the symbol for gravitational potential?

A

V

67
Q

What is the equation for gravitational potential in a radial field?

A

V = -(G M) / r

68
Q

Where is gravitational potential defined as zero?

A

At an infinite distance away from the mass.

69
Q

What does the gradient of a E grav against radius graph represent?

A

The value of the gravitational force at that point.

70
Q

What does the gradient of a V against radius graph represent?

A

The gravitational field strength at that point.

71
Q

What is a satellite?

A

A small mass that orbits a far greater mass.

72
Q

How could you calculate the speed of an orbiting satellite?

A

Equate Newton’s law of gravitation with F = (m v^2) / r and rearrange to make v the subject.

OCR Physics B Unit 4 (5 decks)

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