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A Level Physics Paper 1 > Mechanics > Flashcards

Mechanics Flashcards

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1
Q

Scalar examples

A 
Power
Pressure
Time
Temperature
Volume
Distance
Energy 
Speed
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2
Q

Vector examples

A 
Weight
Velocity
Force
Displacement
Momentum
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3
Q

How do you give the direction of a resultant force

A

Angle

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4
Q

What do you do to find the resultant force if forces aren’t perpendicular

A

Tip-to-tail scale drawing

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5
Q

If a force system is in equilibrium and has two unknown lengths how do you find them

A

Tip to tail scale drawing
Vectors form a closed shape
No resultant force

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6
Q

How can you solve a system in equilibrium

A

Tip to tail scale drawing

Equating horizontal and vertical components

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7
Q

Conditions for equilibrium

A

No resultant force

No resultant moment

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8
Q

What is equilibrium

A

When there is no resultant force
No resultant momentum
So a stationary object stays stationary or moving object stays moving with a constant velocity

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9
Q

Mass vs weight

A

Mass is scalar so only has magnitude whereas weight is a vector so has magnitude and direction
Mass is the amount of material in an object whereas weight is the force exerted by gravity on an object

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10
Q

What is the centre of mass

A

The point through which all the weight is deemed to act

Through which the resultant moment is zero

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11
Q

What is toppling

A

If the weight vector of an object extends outside of its base it will topple

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12
Q

What happens if an objects weight is exactly on the borderline of the base

A

Neither topples or returns to its original position

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13
Q

How do you calculate the maximum angle before toppling on an inclined plane

A

Draw a diagram
Draw a line from centre of object diagonally to edge of corner closes to ground so touching the plane
The lengths of the triangle will be half the height and half the base length/radius
tan-1(radius/half height)

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14
Q

What is a moment

A

The four multiplied by the perpendicular distance from the line of action of the force to the pivot point
Measured in Nm

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15
Q

Moment formula

A

M=Fd

Perpendicular distance

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16
Q

Principle of moments

A

Sum of clockwise moments about any point is the same as the sum of anticlockwise moments about the same point for a body in equilibrium

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17
Q

Uniform

A

Centre of mass is its physical centre

Consistent density

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18
Q

Couple

A

A pair of equal and opposite coplanar forces

Which do not act along the same line of action

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19
Q

Torque

A

Moment of a couple: force multiplied by the perpendicular distance between the lines of action of the forces

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20
Q

Distance

A

Length of path travelled from start to end

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21
Q

Displacement

A

Straight line length in a given direction from start to end point

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22
Q

Velocity

A

Rate of change of displacement

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23
Q

Acceleration

A

Rate of change of velocity

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24
Q

What is earth’s velocity over a year

A

0ms²
Circle
Start is the end
Displacement is zero

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25
Q

Gradient of a displacement time graph

A

Velocity since s/t=v

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26
Q

Gradient of a velocity time graph

A

Acceleration since v/t=a

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27
Q

How does acceleration act in free fall

A

Vertically downwards

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28
Q

Suvat that isn’t given

A

s=vt-1/2at^2

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29
Q

When do you use a suvat

A

Constant acceleration

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30
Q

When do you use speed=distance/time

A

Constant velocity

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31
Q

Examples of free fall

A

Object dropped or thrown down
Object thrown upwards
An object projected in any direction as long as it is not touching anything or any forces acting on it

32
Q

First thing to do before attempting suvat

A

Define positive direction

33
Q

Why does the horizontal component of velocity stay constant

A

There is no horizontal acceleration
If acceleration is zero then velocity remains constant
Air resistance is negligible so only experiences force of weight vertically downwards

34
Q

When is velocity zero at the start of projectile motion questions

A

NEVER

35
Q

When is velocity zero at the end of projectile motion questions

A

NEVER

36
Q

When catching a cricket ball a cricketer moves his hand a short distance in the direction of travel of the ball as it makes contact with his hand. Why

A

There is a larger distance
So the time taken for the momentum to reach zero is increased
If a=v/t, if t increases acceleration decreases
From f=ma, decreasing a decreases the force on his hand

37
Q

What is Newton’s 1st Law of motion

A

If no resultant force is acting on an object
It will either remain at rest
or continue moving with a constant velocity

38
Q

What is Newton’s 2nd Law of motion

A

The rate of change of momentum (acceleration) of a body is directly proportional to the resultant force acting on it

39
Q

How is acceleration related to momentum

A

Rate of change of momentum

40
Q

What is Newton’s 3rd Law of motion

A

When two objects interact they exert an equal and opposite force on each other
The forces are of the same type

41
Q

What is tension

A

A pulling force carried by ropes or cables when taught

42
Q

Where does tension act

A

Away from the points of contact

43
Q

What is free fall

A

I dk check mbook

44
Q

Why can’t you use suvats for terminal velocity

A

Velocity is not constant

45
Q

What is terminal velocity

A

The constant velocity achieved by an object when its drag force is equal in size to the driving force but acting in opposite directions

46
Q

What factors can affect the size of drag

A

Velocity
Cross sectional area
Fluid density
Shape of object

47
Q

Why does an object reach terminal velocity

A

Increased collisions with air particles as velocity increases
So drag increases
Until eventually equal in size to the driving force but in opposite direction

48
Q

Terminal velocity; start of jump

A

Vertical component of velocity is 0
0 air resistance
Fres is weight
Since F=ma, a=9.81ms^-2

49
Q

Terminal velocity; short time after jump

A 
Vertical component of velocity increases
Air resistance increases
Resultant force has decreased
Acceleration less than 9.81
Continues to speed up but at a lesser rate
50
Q

Terminal velocity; eventually (no parachute)

A

As velocity continues to increase so does air resistance
Terminal velocity reached when weight=air resistance
Acceleration is 0
Resultant force is 0
Continues at this speed

51
Q

Terminal velocity; parachute opened

A

Air resistance increases to be larger than the weight
Resistance force acts upwards
Decelerate
Velocity decreases

52
Q

Terminal velocity; after parachute opened

A

Velocity decreases so air resistance decreases
Fres decreases
Deceleration decreases
Slow down at a lesser rate

53
Q

Terminal velocity; eventually (parachute)

A 
Velocity continues to decrease until weight=air resistance= terminal velocity
Acceleration is 0
Resultant force is 0
Continues at this speed
Lower terminal velocity
54
Q

Explain how the resultant force on a car changes as speed increases

A

As speed increases, air resistance increases
So acceleration would decrease
Resultant force decreases because F=ma

55
Q

Explain using Newton’s laws of motion why a vehicle has a maximum speed

A

When the car and the air interact they exert an equal and opposite force on each other (3rd)
As speed increases, air resistance increases
So acceleration would decrease
Resultant force decreases because F=ma
Resultant force = 0
Means car will continue moving at this constant terminal velocity (1st)

56
Q

Units for momentum

A

kgms^-1

Ns

57
Q

Momentum equation

A

mass x velocity

p=mv

58
Q

Equation derivation from N2nd law

A

Change of momentum/time=Resultant force
mv-mu/t=Fres
m(u-v)/t=Fres

Fres= vΔm/Δt

59
Q

How do you handle flow rate questions

A

Consider the fluid after 1 second

60
Q

Impulse

A

Force multiplied by the time for which the force acts
AKA change in momentum
Its a vector

61
Q

Impulse equation

A

I=Δp=Ft

62
Q

Area of a force time graph

A

Impulse

63
Q

Principle of momentum

A

For a system of interacting objects the total momentum remains constant providing no external resultant forces act

(total before=total after)

64
Q

Elastic vs inelastic collision

A

Elastic there is no loss of kinetic energy

Inelastic there is some loss of kinetic energy during the collision

65
Q

Totally inelastic collision

A

Colliding objects stick together

66
Q

How can an inelastic collision be possible if the law of conservation of energy applies

A

Momentum is always conserved in collisions
Total energy is always conserved in collisions
But kinetic energy may be converted to other forms e.g heat

67
Q

Explosion

A

An event where two objects, initially at rest, fly apart f recoil with an equal and opposite amount of momentum

68
Q

Energy is needed for what

A

Moving objects
Heating objects
Changing shapes of objects

69
Q

Principle of conservation of energy

A

Energy cannot be created or destroyed

Only transferred from one type to another

70
Q

Work done

A

Energy given to or removed by a force

71
Q

Work done equations

A

W=Fs

Must be parallel distance so may have to use trig

72
Q

For no loss of energy, energy is as such…

A

Ep at start=Ek at end

mgΔh=1/2mv^2

73
Q

Work done against friction is equal to

A

The difference between initial and final energy

74
Q

Power

A

The rate of transfer of energy

The rate at which work is done

75
Q

Units for power

A

Watts

76
Q

Power equations

A

Power=work done/time
Power=energy transferred/time
Power=force x velocity (Fres=0 and velocity is constant)

A Level Physics Paper 1 (8 decks)

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