Motion Graphs and Forces Flashcards Preview

Physics > Motion Graphs and Forces > Flashcards

Flashcards in Motion Graphs and Forces Deck (105):
1

what does the gradient represent on a distance/time graph?

the gradient is equal to the speed of the object (velocity)

2

what is the equation for speed?

distance ÷ time

3

what is the equation for the average speed?

total distance ÷ total time

4

what does the gradient of a velocity/time graph represent?

the gradient is equal to the acceleration of the object

5

how do you work out the distance travelled on a velocity/time graph?

look at the area under the gradient

e.g. if it makes a triangle under the line you then do 1/2 x base x height to work out the distance

6

what is the units for velocity?

m/s

7

what is the units for acceleration?

m/s2

8

if a ticker tape timer produces dots at a frequency of 50Hz, how many dots are produced per second?

50

9

on a ticker tape timer, how can you tell if the dots are moving at a constant speed?

the dots are equally spready apart

10

on a ticker tape timer, how can you tell if the dots accelerating?

the dots will get further apart

11

on a ticker tape timer, how can you tell if the dots decelerating?

the dots will get closer together

12

what is aceleration?

the rate of change of velocity 

rate of change = 1/t

13

what is the equation for acceleration?

a = v - u ÷ t ( v = final velocity, u = initital velocity)

change in velocity ÷ time taken

a = Δv ÷  t = m/s x 1/s = m/s2

 

14

how do velocity and acceleration act in decelration?

in opposite directions causing the velocity to get smaller

15

what is a scaler quantity?

quantities that have magnitudes or a size only

16

what is a vector quantity?

quantities that have magnitude and direction

17

give some examples of scalars

mass

temprature

distance

time

speed

energy

18

give some examples of vectors

velocity

force

weight

19

what is Newton's first law?

objects will remain at rest or continue to move at a constant speed unless acted upon by a resultant force

if F=0 a =0m/s2

(F = resultant force) 

20

what is Newtons second law?

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

F∝ mv - mu ÷ t 

(F = resultant force, ∝ = directly proportional, t = rate of change, mv - mu = momentum)

F = mv-mu ÷ t 

F = m (v-u) ÷ t [acceleration]

F= ma

resultant force = mass x acceleration

21

what are the units used in the equation for Newton's second law?

resultant force = mass x acceleration​

F = ma

F = resultant force (N)

m = mass (kg)

a = acceleration (m/s2)

22

what is static friction?

the friction acting on stationairy objects

23

what is dynamic friction?

the friction acting on moving objects

24

what is the control variable?

something that is constant and unchanged

25

what is thinking distance?

the distance a vehicle travels while the driver is reacting

26

what is breaking distance?

the distance a vehicle travels while the brakes are being applied until it stops

27

what is stopping distance?

thinking distance + breaking distance

28

give some factors that affect thinking distance

use of alcohol

use of drugs (il/legal)

distracted by passengers in the vehicle

tired

using a mobile

speed of car

 

29

give some factors that affect braking distance

mass of car

weather

tread of tyres

wornout breakes

level of grip on road

speed of car

30

if the distance = 8,000m and the time = 3,600s, calculate the average speed

average speed = total distance ÷ total time

= 8000 ÷ 3600

=2.2 m/s

31

describe the motion of a on this distance/time graph

a is stationairy because the gradient is a straight, vertical  line

 we did not move it we just let the device play

32

describe the motion of e on this distance/time graph

e is accelerating away from the origin

there is no constant speed

we started the pencil case at the device (origin) and then  accelerated it away

33

describe the motion of b and c on this distance/time graph

b is moving fast at a constant speed

c is moving fast at a consant speed but faster than b, almost double

to achieve this graph we flipped the sensor from its side to face upwards and we moved a pencil case upwards and away from it in a constant motion

34

describe the motion of f on this distance/time graph

f is movimg at a fast away from the device (origin) and constant pace but then remains stationairy at a point

35

describe the motion of a on this velocty/time graph

a is moving at a constant speed

36

describe the motion of d on this velocity/time graph

d is deccelerating at a constant rate

37

describe the motion of b and c on this velocity/time graph

b is acelerating at a constant rate

c is acelerating at a constant rate faster than b

38

in equilibrium or when stationionairy or moving a constant speed, what is the resultant force?

0N

39

calculate the resultant force and the accelertaion of this 5.0kg mass

F = 1050-895

= 155N (downwards)

as F = ma

a = F ÷ m

= 155÷5

= 31 m/s2

 

40

calculate the resultant force and the accelertaion of this 5.0kg mass

F = 100 + (-80)

= 20N (to the left)

as F = ma

a = F ÷ m

= 20 ÷ 5

= 4 m/s2 (to the left)

41

calculate the resultant force and the accelertaion of this 5.0kg mass

F = 10 + (-15) 

= 5N (downwards)

as F = ma

a = F ÷ m 

= 5 ÷ 5

=1 m/s2

42

calculate the resultant force and the accelertaion of this 5.0kg mass

F = 100 + (-500)

= 400N (downwards)

as F = ma

a = F ÷ m

= 400 ÷ 5 

=80m/s2 (downwards)

43

what is the reaction time of the driver?

0.6 seconds

44

calculate the thinking distance

area of the rectangle (imagine this)

20 x 0.6 

= 12m 

45

how long did the car brake for?

2.8-0.6

= 2.2 secs

46

calculate the braking distance

area of triangle

0.5 x 20 x 2.2

= 22

47

calculate the stopping distance if it has been previously worked out that the thinking distance is 12m and the braking distance is 22m

22 + 12

= 34m

48

in terms of energy, what do brakes do to a car?

original kinetic energy = 400,000J

final kinetic energy = 0J

kinetic energy is converted into heat and sound which is then disipitated into the atmosphere

the brake pads do work

kinetic energy --> heat + sound

49

if Fd = change in Ek, calculate the average braking force (F) produced by the brakes

kinetic energy = 400,000J

braking distance = 22m

 

d = braking distnace = 22

Ek = 400,000J

F = Ek ÷ d

= 400,000 ÷ 22

= 18181.81 N

 

50

when giving an acceleration, what must it have?

a direction

e.g. downwards, to the left

51

complete this skydiver velocity/time graph

52

state the value or direction of the resultant force at A

Resultant force is acting dowanwards because weight is the only force acting on the sky diver

towards the ground (downwards)

53

state the value or direction of the resultant force at B

resultant force is decreasing yet it still acting downwards because air resistance is increasing

54

state the value or direction of the resultant force at C

resultant force is zero

the skydiver has reached terminal velocity

because the graident and acceleration is zero

55

state the value or direction of the resultant force at D

 

resultant force is acting upwards (velocity acting down, accelerating upwards)

because he is rapidly deccelertaing

56

state the value or direction of the resultant force at E (end of graph parachute)

resultant force is zero as the sky diver has reached a new terminal velocity

because the gradient and acceleration is zero

57

the weight of an object is the force of ......which acts on it

gravity

58

when you drop something, first of all it .....

acelerates

59

the faster an object falls, the bigger force of ....... which acts on it

friction

60

eventually a dropped object will .......

fall at a steady speed

61

which force is the foward force from the engine?

which force is the force resisting the van's motion?

A is the foward force

E is the force resisting motion

62

complete this table

63

complete the following paragraph to explain why seatbelts reduce the risk of injury if the van stops suddenly

a large .... is needed to stop the van suddenly

the driver and passengers would continue to move .....

the seatbelts supply a .... force to keep the driver and passengers in their seats

a large force is needed to stop the van suddenly

the driver and passengers would continue to move fowards

the seatbelts supply a backwards force to keep the driver and passengers in their seats

64

if the mass of a car is 950kg and the car can accelerate from 0 to 33m/s in 11 seconds, calculate the acceleration of the car during the 11 scesonds

a = v-u ÷ t 

= 33 - 0 ÷ 11

= 3m/s2

65

if the mass of a car is 950kg and the car can accelerate from 0 to 33m/s in 11 seconds, calculate the force needed to produce this acceleration

F = ma

= 950 x 3

=2850 N

66

The manufactor of a car claims a top speed of 110 miles per hour. Explain why there must be a top speed for a car

the air resistance will increase directly proportionally to the speed

the car cannot accelerate forever, it must reach a resultant force 

everntually the engine force will = air resistance

67

a driver may have to make an emergency stop

give three factors which affect their thinking distance or braking distance

use of alcohol affects thinking distance as it slows down you reaction time. this affects your stopping distance as stopping distance = thinking + braking distance. if your thinking distance increases, so will your stopping distance

being distracted by the passengers in the car will affect thinking disatnce as you aren't focused and your reaction time is delayed - this increased stopping distance as they are connected

worn out brakes will affect your braking distances as the efficiency of the brakes decreases . friction will act in opposite motion to the tyres, increasing the braking distance. as braking distance increases, so does stopping

68

what does the acceleration of a car depend on?

the force applied by the engine and the mass of the car

69

the velocity of a car is its speed in a particular ......

direction

70

what part of the graph represents thinking time of the driver and what is this time in seconds?

A - B

0.7 seconds

71

calculate the distance travelled by the car in thinking time

area of rectangle

0.7 x 24

= 16.8m

 

72

calculate the acceleration of the car after the brakes are applied

a = v - u ÷ t 

= 24 ÷ t 

= -6 m/s2

73

calculate the distance travelled by the car during braking

are under the traingle

4x 24 ÷ 2 

= 48m

74

the mass of the car is 800kg

calculate the braking force

F = ma

= 800 x -6

= - 4800 N

75

Explain the motion of a skydiver

Before the parachute opens:

1. When the skydiver jumps out of the plane he accelerates due to the force of gravity pulling him down.

2. As he speeds up the upwards air resistance force increases. He carries on accelerating as long as the air resistance is less than his weight.

3. Eventually, he reaches his terminal speed when the air resistance and weight become equal. They're said to be balanced.

After the parachute opens:

4. When the canopy opens it has a large surface area which increases the air resistance. This unbalances the forces and causes the parachutist to slow down.

5. As the parachutist slows down, his air resistance gets less until eventually it equals the downward force of gravity on him (his weight). Once again the two forces balance and he falls at terminal speed. This time it's a much slower terminal speed than before.

76

Look In Experiment Write-Ups:

describe an experiment to investigate friction

77

Define resultant force

the sum forces acting on an object

78

What is the equation that links gravity, mass and weight?

weight (N) = mass (kg) x gravity (N/kg)

79

What are the units for force?

Newtons (N)

80

What are the units for acceleration?

Metres per second2 (m/s2)

81

What are the units for gravity?

Netwong per kilogram (N/kg)

82

What are the units for mass?

Kilograms (kg)

83

A force is simply a ... or a ...

A force is simply a push or a pull

84

What are the twelve different types of forces you need to know?

gravity

weight

reaction force

electrostatic force

thrust

push

pull

drag

air resistance

friction

lift

tension

85

Gravity or weight always act ...

Gravity or weight always act straight downwards

86

Reaction force from a surface usually acts ...

Reaction force from a surface usually acts straight upwards

87

The direction of electrostatic force between two charged objects depends on ...

The direction of electrostatic force between two charged objects depends on the type of the charge (like charges repel, opposite charges attract) 

88

Thrust or push or pull speeds/slows something up/down

Thrust or push or pull speeds something up

89

Drag or air resistance or friction speeds/slows something up/down

Drag or air resistance or friction slows something down

90

Lift acts on ...

Lift acts on aeroplane wings

91

Tension acts in a ... or ...

Tension acts in a rope or cable

92

What four forces are acting on a moving car?

93

If an object has no force propelling it foward, it will always slow down and stop because of ...

 

If an object has no force propelling it foward, it will always slow down and stop because of friction

94

What is friction?

friction is a force that opposes motion

95

In what three main ways does friction occur?

Friction betwen solid surfaces which are gripping (static friction)

Friction between solid surfaces which are sliding past each other

Resistance or 'drag' from fluids (liquids or gases)

96

How do you reduce:

Friction betwen solid surfaces which are gripping (static friction)

Friction between solid surfaces which are sliding past each other

by putting a lubricant, like oil or grease, between the surfaces

97

In a fluid, friction always increases as the speed ...

In a fluid, friction always increases as the speed increases

98

Explain how moving objects reach a terminal velocity

Wehn objects first set off they have much more force accelerating them than resistance slowing them down

As the velocity increases, the resistance increases

This gradually reduces the acceleration until eventually the resistance is equal to the accelerating force and then it won't be able to accelerate any more - it will have reached its terminal velocity

99

How can you investigate falling objects using sycamore seeds?

1. Sycamore seeds have a small wieght and a large surface area so they reach terminal velocity really quickly and fall slowly

2. Collect a bunch of sycamore seeds of different sizes and measure the mass and wing length of each one. Use an accurate ruler and repeat each measurement several times to make sure it's accurate. Use all the seeds that have similar masses but different wavelengths

3. Drop each of the seeds from the same height and use a stopwatch to find how long each one takes to fall to the ground. The higher you drop them the better - it gives a larger measurement and so improves the accuracy of the measurement

4. Repeat the experiment for each seed and find an average time

5. Plot a graph of length of the wings (x) against the time taken to hit the floor (y). This will tell you if there is a relationship between the shape of the sycamore seeds and their terminal velocity

6. Bigger wings means bigger surface area and so higher drag. Higher drag means lower terminal velcoty, and so the seeds fall more slowly

100

Explain the relationship between drag (air resistance) and weight during terminal velocity

during terminal velocity, weight = drag (air resistance)

101

What is Newton's Third Law?

if object A exerts a force in object B then object B exerts the exact opposite force on object A

102

Objects ... when the resultant force is positive

Objects ... when the resultant force is negative

Objects accelerate when the resultant force is positive

Objects decelerate when the resultant force is negative

103

Be able to describe the motion of objects on a distance/time graph

104

Be able to describe the motion of objects on a velocity/time graph

105

Describe an experiment to investigate the motion of a toy car on a ramp

1. Mark a line on the ramp - this is to make sure the car starts from the same point each time

2. Measure the distance between each light gate - you'll need this to find the car's average speed

3. Let go of the car just before the light gate so that it starts to roll down the slope

4. Let go of the car just before the light gate so that it starts to roll down the slope

5. The light gates should be connected to a computer. When the car passes through each light gate, a beam of light is broken and a time is recorded by a data-logging software

6. Repeat this experiment several times and get an average time for the car to reach each light. This will make your results more reliable

7. Using these times and distances between lightgates you can find the average speed of the car on the ramp and the average speed of the car on the runway