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CGP PHYSICS > Chapter 11 - momentum etc > Flashcards

Chapter 11 - momentum etc Flashcards

1
Q

What is the symbol for momentum?

A

p

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2
Q

What is the equation for momentum?

A 
momentum = mass * velocity
P = mv
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3
Q

Is momentum a vector or scalar quantity?

A

vector

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4
Q

What is a vector quantity?

A

A quantity with a magnitude and a direction

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5
Q

What is always conserved in a collision?

A

momentum and energy

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6
Q

What must the total momentum be after a collision?

A

Equal to the total momentum before (to conserve momentum)

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7
Q

How is a rocket propelled in space?

A

The rocket ejects exhaust gases which travel away from the rocket with a velocity and so momentum
To conserve momentum, the momentum after ejection must equal zero
To achieve this the rocket moves away in the opposite direction, with an equal but opposite momentum

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8
Q

What is Newton’s first law of motion?

A

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

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9
Q

What is acceleration?

A

A change in speed or a change in direction

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10
Q

What causes an acceleration?

A

A resultant force

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11
Q

What is Newton’s second law?

A

The rate of change of momentum is directly proportional to the resultant force which acts on the object

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12
Q

What is Newton’s second law as an equation?

A 
Force = change in momentum/time
F = Δp/Δt
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13
Q

If the mass is constant, how can Newton’s second law be written?

A

resultant force = mass * acceleration

F=ma

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14
Q

In what direction will an acceleration always be?

A

The same direction as the resultant force which caused it

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15
Q

When does F=ma not work?

A

When an object is accelerating at close to the speed of light, so its mass is changing

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16
Q

What is Newton’s third law?

A

If an A object exerts a force on object B, then object B will exert an equal and opposite force on object A

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17
Q

What type must the two forces in a pair be for Newton’s third law?

A

They can be any type but the two forces in the pair have to be of the same type
eg both electrical forces or both gravitational forces

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18
Q

Why is a book resting on a table not an example of Newton’s third law?

A
  • Both forces are acting on the same object

- The forces are not the same type

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19
Q

When is work done?

A

When energy is transferred

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20
Q

What is work?

A

The amount of energy transferred from one form to another when a force causes some kind of movement

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21
Q

What is the equation for work?

A 
work = force * distance moved in the direction of force
W = Fs
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22
Q

What is the symbol for work?

A

W

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23
Q

What are the units of work?

A

J

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24
Q

What is the definition of one joule?

A

The work done when a force of 1N moves an object through a distance of 1m

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25
How can work done be found graphically?
The area under a force vs distance moved graph
26
What is the equation for force used if the direction of movement is not in the same direction as the direction of force?
W = Fscosθ
27
What is the principal of conservation of energy?
Energy cannot be created or destroyed. Energy can be transferred from one form to another but the total amount of energy in a closed system will not change.
28
What is the formula for efficiency?
efficiency = useful power output/total power input
29
What is the formula for power?
power = work done/time
30
What are the two equations for kinetic energy?
E = 1/2mv^2 | E =p^2/2m
31
What is the equation for gravitational potential energy?
E = mgΔh
32
What is the equation for elastic potential energy?
E = 1/2kx^2
33
How many radians are there in one complete circle?
2π
34
How do you convert from degrees to radians?
multiply by 2π/360
35
How do you convert from radians to degrees?
divide by 2π/360
36
What is 45 degrees in radians?
π/4
37
What is 90 degrees in radians?
π/2
38
What is 180 degrees in radians?
π
39
What is angular speed?
The angle an object rotates through per second
40
What are the units of angular speed?
radians per second | rads^-1
41
What is the equation linking angular speed, angle and time?
ω = θ/t
42
What is the equation linking linear speed and angular speed?
v = ωr
43
What is another word for the linear speed?
tangential velocity
44
Why are objects travelling in a circle accelerating, even when they travel at a constant speed?
They are constantly changing direction
45
What is the name for the acceleration found in objects travelling in a circle?
centripetal acceleration
46
In what direction is centripetal acceleration?
Towards the centre of the circle
47
What are the two equations for the centripetal acceleration?
``` a = V^2/r a = ω^2 r ```
48
What is the centripetal acceleration produced by?
A centripetal force
49
What are the two equations for the centripetal force?
F = mv^2/r F =mω^2 r (both derived from F=ma)
50
What happens when an object with mass is put into a gravitational field?
It experiences an attractive force
51
What kind of force is always experienced by a mass in a gravitational field
attractive
52
What are point masses?
Objects that behave as if all of their mass is concentrated at the centre (eg uniform spheres)
53
What is Newton's law of gravitation?
F = -GMm/r^2
54
For gravitational fields, are attractive forces thought of as positive or negative?
negative | repulsive forces are positive
55
What is G?
The gravitational constant | 6.67 x10^-11
56
What are the units of the gravitational constant?
Nm^2kg^-2
57
What is the inverse square law for Newton's law of gravitation?
F ∝ 1/r^2
58
If the distance between two masses doubled, what would happen to the force experienced?
It would be one quarter of the strength of the original force
59
What are gravitational lines of force?
'field lines' for gravitational fields | Arrows showing the direction of the force a mass would feel in the gravitational field
60
What do the directions of arrows on gravitational field lines show?
The direction of a force a mass would experience if it were at that point in the gravitational field
61
What does it mean if the gravitational line of force are closer together?
The force experienced is stronger
62
What do the gravitational field lines of a uniform field look like?
Evenly spaced
63
Where can you treat the Earth's gravitational field as uniform?
Close to the Earth's surface | the field lines are almost parallel here
64
What shape is Earth's gravitational field?
radial | field lines meet at the centre of the Earth
65
What is the gravitational field strength?
The force per unit mass
66
What is the symbol for gravitational field strength?
g
67
What is the equation for gravitational field strength?
g = F/m
68
What are the units of g?
Nkg^-1
69
Is g negative or positive?
negative
70
Is g a vector or a scalar?
vector
71
In what direction does g always point?
Towards the centre of mass whose field is being described
72
What is another term for the gravitational field strength?
Acceleration due to gravity, g
73
What is the value of g at Earth's surface?
-9.8 Nkg^-1
74
In what kind of field will a constant force be experienced?
A uniform field
75
What is the equation for force experienced by a mass in a gravitational field?
F = mg
76
What is the equation for gravitational potential energy?
ΔPE = mgΔh
77
What kind of gravitational field to point-like masses have?
radial
78
How can gravitational potential be found graphically?
The area under a g vs r graph
79
What is the inverse square law which gives g?
g = -GM/r^2
80
When is gravitational potential energy gained?
When you move away from the centre of mass
81
What is the gravitational potential energy of an object?
The work that would need to be done against the force of gravity to move the mass beyond the gravitational field (ie to infinity)
82
What is the equation for gravitational potential energy?(not PE = mgh)
E = -GMm/r
83
Why is gravitational potential energy negative?
It is an energy debt, the energy which would be needed to move the mass out of the field
84
Where is potential energy zero?
At an infinite distance from the centre of mass (eg the Earth)
85
How can the gravitational force be found graphically?
The tangent of a potential energy vs radius graph
86
What is gravitational potential?
The potential energy per unit mass
87
What is the symbol for gravitational potential?
V
88
What is the equation for gravitational potential?
V = GPE/m
89
What is the equation for gravitational potential in a radial field? (not PE/m)
V = -GM/r
90
Where is gravitational potential zero?
At infinity
91
How can g be found graphically?
The gradient of a tangent to a graph of V vs r
92
What do equipotentials show?
All points in a field which have the same potential, V
93
What happens to your energy if you travel along an equipotential?
It does not change
94
What is the relationship between equipotentials and field lines?
They are perpendicular
95
What is a satellite?
A smaller mass that orbits a much larger mass
96
What is the equation for the speed of an orbiting mass?
V = √(GM/r)
97
What is the equation for the escape velocity of an object?
v = √(2GM/r)
98
When would an object be able to escape a gravitational field?
When its kinetic energy is greater than or equal to its gravitational potential energy (ie if it is travelling fast enough)

CGP PHYSICS (8 decks)

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