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AS-Level Physics > Mechanics > Flashcards

Mechanics Flashcards

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1
Q

What is a vector quantity?

A

A physical quantity with magnitude and direction.

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2
Q

What is a scalar quantity?

A

A physical quantity with only magnitude.

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3
Q

Give three examples of scalar quantities.

A
  • Distance
  • Speed
  • Mass
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4
Q

Give five examples of vector quantities.

A
  • Displacement
  • Velocity
  • Acceleration
  • Momentum
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5
Q

When can vector quantities be added together?

A

When the vectors are parallel or antiparallel.

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6
Q

How can resultant vectors be calculated?

A
  • Scaled diagram
  • Pythagoras
  • Trigonometry
  • Resolve components
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7
Q

How are vectors added using a scaled diagram?

A
  • The vectors are drawn to scale and joined head to tail in the correct direction.
  • The resultant vector joins the polygon.
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8
Q

What are the components of a vector?

A

The perpendicular pair of vectors.

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9
Q

How can vectors be added by resolving components?

A
  • The vertical and horizontal components of the vectors are calculated.
  • The perpendicular components are added and the resultant vector calculated.
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10
Q

What is the component parallel to the slope of a weight?

A

mgsinx

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11
Q

What is the component perpendicular to the slope of a weight?

A

mgcosx

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12
Q

Which forces acting on a weight are parallel to the slope?

A
  • Friction

- Weight component

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13
Q

Which forces acting on a weight are perpendicular to the slope?

A
  • Normal reaction force

- Weight component

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14
Q

What is a moment?

A

A force that produces a turning effect given by force x perpendicular distance from the line of action of the force to the pivot.

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15
Q

What is a moment also known as?

A

Torque

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16
Q

How can a moment be increased?

A
  • Increased force

- increased distance

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17
Q

What is the principle of moments?

A

At balance, the sum of the clockwise moments about a point is equal to the sum of the clockwise moments about the same point.

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18
Q

What is the centre of gravity?

A

The point from which all the weight of an object appears to from.

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19
Q

Explain how the centre of gravity of a lamina can be found.

A
  • Make a small hole in the corner of the shape and suspend it from a pin so it can move freely.
  • Hang a plumb line from the pin and mark the vertical line.
  • Repeat for two more points.
  • The point of intersection shows the centre of gravity.
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20
Q

How can an object be made stable?

A
  • Low centre of mass.

- Large base area.

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21
Q

When will an object tip over?

A

When the centre of gravity passes outside the base.

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22
Q

What is statics?

A

The study of forces acting on stationary objects.

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23
Q

What is Newtonian mechanics?

A

The study of objects that obey Newton’s three laws of motion.

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24
Q

Define coplanar forces.

A

Forces that all act in the same plane.

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25
Q

What happens when the vectors acting on a point form a closed polygon?

A

There is no resultant vector.

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26
Q

Give the two conditions for static equilibrium of coplanar forces.

A
  • The resultant vector must be zero.

- The principle of moments must apply.

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27
Q

What is the principle of concurrency?

A

For three coplanar forces in equilibrium, the lines action must all pass though one point. (be concurrent)

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28
Q

What does the principle of concurrency apply to?

A

An object acted on by three forces.

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29
Q

Define dynamics.

A

The study of forces that may result in motion.

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30
Q

What happens if there is no resultant force on an object?

A

There is no change in velocity.

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31
Q

What is Newton’s first law?

A

An object will remain at rest or in uniform motion unless acted on by an unbalanced force.

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32
Q

What is Newton’s second law?

A

The resultant force is directly proportional to the rate of change of momentum.

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33
Q

What is Newton’s third law?

A

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

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34
Q

What are the two factors that affect the acceleration of an object?

A
  • The size of the resultant force.

- The mass of the object.

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35
Q

What is relationship between resultant force, mass and acceleration?

A

F = ma

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36
Q

How is weight calculated from mass?

A

W = mg

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37
Q

What are the two forces acting on a falling object?

A
  • Weight

- Air resistance

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38
Q

How does air resistance change with velocity?

A

Air resistance increases as velocity increases.

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39
Q

Describe the changes in velocity of a parachutist.

A
  • There is an initial acceleration of g.
  • Acceleration decreases until the terminal velocity is reached.
  • Once the parachute is opened there is a large deceleration.
  • Deceleration decreases until the terminal velocity is reached.
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40
Q

What are the two rules of Newton’s third law?

A
  • The forces act on different objects.

- The forces must be the same type.

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41
Q

Which two forces act on an object sitting on the ground?

A
  • Weight

- Reaction force

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42
Q

What causes a person to feel weightless?

A

When the reaction for is less than the weight.

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43
Q

How is average speed calculated?

A

distance travelled / time taken

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44
Q

What two things can the gradient of a distance vs. time graph show?

A
  • Speed

- If the gradient is constant the speed is constant.

45
Q

What does the area under a speed vs. time graph show?

A

Distance travelled

46
Q

What does the gradient of a displacement vs. time show?

A

Velocity

47
Q

What does a negative gradient on a displacement vs. time graph show?

A

The direction of travel has changed.

48
Q

What does the area under a velocity vs. time graph show?

A

Displacement

49
Q

What does the gradient of a velocity vs. time graph show?

A

Acceleration

50
Q

Why is an object moving in a circle constantly accelerating?

A
  • Acceleration is given by change of velocity.

- If the object is moving in a circle, the velocity is changing.

51
Q

What are the four SUVAT equations?

A

s=([u+v]/2)t
v=u+at
s=ut+0.5at^2
v^2=u^2+2as

52
Q

How is kinetic energy calculated?

A

1/2mv^2

53
Q

How is GPE calculated?

A

mgh

54
Q

How is change in GPE calculated?

A

mgΔh

55
Q

How is velocity calculated from KE and GPE?

A

v=(2gh)^2

56
Q

How is work done calculated?

A

force x displacement of the force

57
Q

What is work done equivalent to?

A

Energy transferred

58
Q

How is efficiency calculated?

A

(useful energy out / total energy in) x 100%

59
Q

What is power?

A

The rate of energy transfer

60
Q

How is power calculated?

A

energy transferred / time taken
or
force x velocity

61
Q

How is momentum calculated?

A

mass x velocity

62
Q

What is the unit of momentum?

A

kgm/s

63
Q

What type of quantity is momentum?

A

Vector

64
Q

What is the rate of change of momentum equal to?

A

The resultant force causing it.

65
Q

What is the change in momentum of an object experiencing a force equal to?

A

The impulse acting on the object.

66
Q

What is the unit of an impulse?

A

Ns / kgm/s

67
Q

What does the area under a force vs. time graph give?

A

Change in momentum

68
Q

How do crumple zones improve car safety?

A

The rate of change of momentum is reduced which reduces the force acting on the car.

69
Q

What three car safety features utilise the fact that rate of change of momentum = force?

A
  • Crumple zones
  • Seatbelts
  • Airbags
70
Q

What is the law of conservation of momentum?

A

In any collision in which no external forces act, the total momentum before the collision is equal to the total momentum after the collision.

71
Q

What is an elastic collision?

A

One in which kinetic energy as well as momentum is conserved.

72
Q

What happens to a body in stable equilibrium when displaced then released?

A

It returns to its equilibrium position.

73
Q

When will an object tilt?

A

When Fd>Wb/2

74
Q

What three principles apply to all projectiles?

A
  • The acceleration of the object is always equal to g.
  • The horizontal velocity is constant.
  • The motions in the horizontal and vertical directions are independent.
75
Q

What happens to the path of a stone thrown from a cliff if the initial projection is horizontal?

A
  • The path becomes steeper as it drops.
  • The faster it is projected, the further away it will fall.
  • The time taken for it to fall doesn’t depend on how fast it is projected.
76
Q

What is rocket thrust equal to?

A

T=mg+ma

77
Q

What three things does drag force depend on?

A
  • Shape of the object
  • Speed
  • Viscosity of fluid.
78
Q

What is thinking distance?

A

The distance travelled by a vehicle in the time it takes the driver to react.

79
Q

How is thinking distance calculated?

A

s = speed x reaction time

80
Q

How is braking distance calculated?

A

s = v^2/2a

81
Q

How is stopping distance calculated?

A

vt + v^2/2a

82
Q

How is impact time calculated?

A

t = 2s/u+v

83
Q

How is impact force calculated?

A

F = change in Ek / impact distance

84
Q

Give five car features that increase impact time.

A
  • Bumpers
  • Crumple zones
  • Seat belts
  • Collapsible steering wheel
  • Airbags
85
Q

How is work done calculated?

A

force x distance moved in the direction of the force

86
Q

How is motive power calculated?

A

energy per second wasted + gain of kinetic energy per second

87
Q

How is the power generated from a wind turbine generated?

A

0.5ρv^3A

88
Q

How is the power generated from a hydroelectric power station generated?

A

P=ηρgh

η=efficiency

89
Q

How much energy can 1m^2 of a solar panel absorb in space?

A

1400J/s

90
Q

How is density calculated?

A

ρ=m/V

91
Q

How is the density of an alloy calculated?

A

ρ = ρAVA/Vtotal + ρBVB/Vtotal

92
Q

What is Hooke’s Law?

A

The force needed to stretch a spring is directly proportional to the extension of the spring.

93
Q

How is the force needed to stretch a spring calculated?

A

F = kΔL

94
Q

What is the unit of spring constant?

A

N/m

95
Q

What happens when a spring is stretched beyond its elastic limit?

A

It never regains its original length when the force is removed.

96
Q

What is the spring constant?

A

Force required to extend a spring by 1m.

97
Q

What is the effective spring constant of two springs in parallel?

A

2k

98
Q

What is the effective spring constant of two springs in series?

A

k/2

99
Q

How is the effective spring constant of two springs in constant calculated?

A

1/k = 1/kp + 1/kq

100
Q

How is the elastic potential energy stored in a stretched spring calculated?

A

0.5kΔL^2

101
Q

What is the elasticity of a material?

A

Its ability to regain its shape after being deformed.

102
Q

What can be used to measure the extension of a wire under tension?

A

Searle’s apparatus

103
Q

How is tensile stress calculated?

A

σ = T/A

104
Q

How is tensile strain calculated?

A

ε = ΔL/L

105
Q

What is the Young modulus of a material?

A

The tensile stress divided by the tensile strain.

106
Q

How is the cross section area calculated for a wire?

A

A = πd^2 / 4

107
Q

What is the yield point?

A

The point at which the wire temporarily weakens.

108
Q

What is a ductile material?

A

A material which exhumes plastic behaviour.

109
Q

How is the elastic energy stored in a stretched wire calculated?

A

0.5TΔL

AS-Level Physics (4 decks)

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