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AQA A-level Physics > Mechanics > Flashcards

Mechanics Flashcards

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1
Q

What is a vector quantity?

A

a physical quantity with direction AND magnitude

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2
Q

What are some examples of vector quantities? (5)

A

force
acceleration
displacement
momentum
velocity

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3
Q

What is a scalar quanitity?

A

a physical quantity that is NOT directional and has a magnitude ONLY

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4
Q

What are some examples of scalar quantities? (5)

A

distance
speed
mass
temperature
energy

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5
Q

What is displacement?

A

a vector quantity- describes how far an object is from where it started and in what direction

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6
Q

How can we combine vectors?

A

-use Pythagoras’ theorem (for two vectors acting at right angles to each other)

-use a scale drawing, find angles using a protractor and use the sine/cosine equation (for vectors not at right angles)

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7
Q

What do we mean by coplanar forces?

A

forces which act in the same plane

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8
Q

How can we resolve vectors? Give the equations to find out the Fx and Fy vectors

A

use trigonometry
-for the horizontal component, Fx = F cos θ
-for the vertical component, Fy = F sin θ

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9
Q

How are vectors resolved on a slope?

A

usually need to resolve weight:
- W cos (θ) perpendicular to the slope
- W sin (θ) parallel to the slope

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10
Q

What does it mean if an object is at equilibrium?

A

-at rest
-no resultant force
-constant velocity

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11
Q

What does it mean if a vector triangle is closed?

A

the forces are at equilibrium

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12
Q

What is a moment?

A

the force multiplied by the perpendicular distance from the line of action of the force to the pivot

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13
Q

What is the equation to calculate the moment of a force? Include units

A

M=Fd

where:
M= moment (Nm)
F= force (N)
d= perpendicular distance from the line of action from the force to the pivot (m)

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14
Q

What do the principle of moments state?

A

at EQULIBIRBIUM, the sum of the clockwise moments= the sum of the anti-clockwise moments ABOUT A GIVEN POINT

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15
Q

What do we mean by the centre of mass?

A

the point at which the entire WEIGHT of an object can be considered to ACT THROUGH

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16
Q

What is a couple?

A

a pair of forces of equal magnitude acting antiparallel either side of a pivot

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17
Q

What mnemonic is used for the equations of motion?

A

SUVAT

where
s= displacement (m)
u= initial velocity (ms^-1)
v= final velocity (ms^-1)
a= acceleration (ms^-2)
t= time (s)

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18
Q

How can we work out acceleration if we have 2 velocity’s and 2 times?

A

-same as a gradient of a velocity-time graph
change in velocity/ change in time

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19
Q

How can we work out velocity if we have two displacements and two times?

A

-same as a gradient of a displacement-time graph
change in displacement/ change in time

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20
Q

What doe we mean by instantaneous velocity?

A

the velocity of an object at a specific point in time

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21
Q

How can we work out the average speed/velocity?

A

velocity:
total displacement/ total time taken

speed:
total distance/ total time taken

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22
Q

What is the gradient of a displacement-time graph at a specific point equal to?

A

instantaneous velocity

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23
Q

What is the gradient of a velocity-time graph equal to?

A

acceleration

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24
Q

What is the area under a velocity-time graph equal to?

A

overall displacement

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25
Q

What is the area under an acceleration-time graph equal to?

A

overall change in velocity

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26
Q

When do we use SUVAT equations?

A

when the acceleration is uniform and resultant force is constant

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27
Q

Name all the SUVAT equations (4)

A

v= u + at
s= 1/2(u + v) x t
v^2= u^2 - 2as
s= ut + 1/2at^2

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28
Q

What is something to know when an object is being projected?

A

the horizontal and vertical components need to be treated independently

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29
Q

What do we mean by time of flight?

A

how long the projectile is in the air

30
Q

What do we mean by the maximum height?

A

the height at which the projectile is momentarily at rest

31
Q

What do we mean by the range?

A

the horizontal distance travelled by the projectile

32
Q

What do you do if a projectile is at an angle and with a velocity acting in that direction?

A

resolve the vectors

33
Q

How do you work out time of flight?

A

2 x time taken to reach maximum height

34
Q

How can you find the time taken to reach maximum height?

A

use the SUVAT equations

35
Q

When working with projectiles, what component is always zero for the x-components?

A

acceleration

36
Q

When working with projectiles/free fall, what would acceleration be for the y-component?

A

if up is the +ve:

if moving up: 9.81
if moving down: -9.81

37
Q

What are the two types of resistive forces?

A

-contact friction
-fluid friction/drag

38
Q

What increases fluid friction/drag? (3)

A

-increasing viscosity of fluid
-increasing speed of the object relative to the fluid
-increasing the cross-sectional area of object pushing through the fluid

39
Q

What is lift?

A

an upwards force on an object moving through a fluid. It is perpendicular to the fluid flow

40
Q

What is thrust?

A

direction of motion

41
Q

What is the effect of having/not having air resistance in projectile motion?

A

no air resistance:
range and maximum height is increased compared

with air resistance:
lower maximum height, smaller range (proj. diagram would have an asymmetrical and lower parabola compared to no air resistance)

42
Q

What is terminal velocity? When does it occur?

A

the maximum velocity an object can have
- occurs when resistive forces balance the driving forces

43
Q

RP3: describe this practical

A

-aim of the experiment is to calculate the value of the acceleration due to gravity, g
-done by measuring the time it takes for a ball-bearing to fall a certain distance. The acceleration is then calculated using an equation of motion

44
Q

RP3: what should the graph be? Write the equation of the line

A

2h/t= gt +2u

where:
y = 2h/t (m s-1), velocity
x = time
m = g(m s–2), acceleration
y-intercept = 2u, initial velocity

45
Q

What does Newton’s 1st law state?

A

the velocity of an object will not change unless acted on by a resultant force

46
Q

What does Newton’s 2nd law state? Write down the equation with units

A

the resultant force on an object is equal to its rate of change in momentum

F= change in momentum/change in time

where:
F= resultant force (N)
momentum= kgms^-1
time= s

47
Q

What equation can you use from Newton’s 2nd law for a constant mass?

A

F= ma

where
f= resultant force (N)
m= mass (kg)
a= acceleration (ms^-2)

48
Q

What equation can you use from Newton’s 2nd law for a constant velocity?

A

F= v(change in mass/ change in time)

where:
F= resultant force (N)
v= velocity (ms^-1)
mass= kg
time= s

49
Q

What does Newton’s third law state?

A

when one body exerts a force on a second body, the second body simultaneously exerts a force of equal magnitude and opposite direction to the first body

50
Q

How can we calculate momentum?

A

p= mv

where:
p= momentum (kgms^-1)
m= mass (kg)
v= velocity (ms^-1)

51
Q

What is the principle of conservation of momentum?

A

the total momentum before a collision = the total momentum after a collision provided no external force acts

52
Q

What is impulse?

A

change in momentum

53
Q

What are the equations to work out impulse? What is its unit?

A

impulse (Ns) = force x change in time
or
impulse (Ns) = change in momentum

54
Q

When are the impulse equations used?

A

when force is constant

55
Q

How can we work out impulse from a force-time graph?

A

area of the graph

56
Q

What is something to know about energy?

A

total energy is always conserved

57
Q

What does the principle of the conservation of energy state?

A

energy cannot be created or destroyed, only be transferred from one store to another

58
Q

What do we mean by an elastic collision?

A

when there is no loss of kinetic energy in the collision

59
Q

What do we mean by an inelastic collision?

A

when the colliding objects have less kinetic energy than before

60
Q

What happens to the kinetic energy in an inelastic collision?

A

some of the energy will be shifted to the surroundings e.g thermal stores

61
Q

What does it mean if objects couple together after a collision?

A

they must have undergone an inelastic collision

62
Q

What is work?

A

the amount of energy transferred when an external force causes an object to move over a certain distance

63
Q

How can we calculate the work done?

A

W=fs

where:
W= work done (J)
f= force (N)
s= displacement (m)

64
Q

How can you calculate the work done of the force is at an angle?

A

W = Fs cos θ (or sin θ)

65
Q

How can you find the work done from a force-displacement graph?

A

find the area

66
Q

What is power?

A

the rate of energy transfer

67
Q

How can we calculate power?

A

Power (W) = change in work done/ change in time

68
Q

How can we calculate power if an object is moving at a constant velocity with a constant force?

A

P=Fv

where
P= power (W)
F= force (N)
v= velocity (ms^-1)

69
Q

What does the force need to be in order to use the P=Fv equation?

A

must be in the direction of the velocity

70
Q

What is efficiency?

A

How useful something is/how efficient it is

71
Q

What are the two equations to calculate efficiency?

A

(useful power output/total power input) x 100
or
(useful energy output/total energy input) x 100

AQA A-level Physics (11 decks)

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