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A Level Physics > Module 3: Chapter 3 - Motion > Flashcards

Module 3: Chapter 3 - Motion Flashcards

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1
Q

What is the equation for average speed?

A

average speed = Δdistance / Δtime

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2
Q

What is distance?

A

Distance is a scalar quantity and is the length of a route through space

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3
Q

What is displacement?

A

Displacement is a vector quantity and is the distance in a given direction. It describes the position pf one point in space relative to another

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4
Q

Describe the velocity of a car moving at a constant speed in a circular motion.

A

Although the car is travelling at a constant speed, it’s velocity is constantly changing as its direction is constantly changing. Therefore the car is constantly accelerating.

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5
Q

What is speed?

A

Speed is a scalar quantity and is the distance travelled per unit time. It describes the rate of change of distance

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6
Q

What is velocity?

A

Velocity is a vector quantity and is the displacement travelled per unit time. It describes the rate of change of displacement

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7
Q

What is instantaneous speed?

A

The speed at a given moment of time

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8
Q

What is acceleration?

A

The rate of change of velocity

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9
Q

What is a component vector?

A

One of 2 or more vectors into which another vector can be separated

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10
Q

What are the suvat equations (definition)?

A

4 Standard equations describing motion under constant acceleration

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11
Q

What are the 4 suvat equations?

A
  • v = u + at
  • s = ut + ½ at²
  • v² = u² + 2as
  • s = ½(u + v)t
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12
Q

What is direction?

A

A line along which a vector points, given as an angle or a compass point

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13
Q

What is magnitude?

A

The size or quantity, independent of direction or units

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14
Q

What is a parabola?

A

The characteristic path followed by an object moving under gravity in a uniform gravitational field

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15
Q

What is a projectile?

A

An object which is given an inital force and then allowed to move freely under gravity

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16
Q

What the range (of a projectile)?

A

The horizontal distance from its starting point at which a projectile will land.

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17
Q

What is the resultant vector?

A

The vector obtained from the sum. of 2 or more vectors

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18
Q

What is trajectory?

A

The path that an object follows through space, due to the forces that act upon it. Under the influence of gravity, projectiles in freefall will follow a parabolic trajectory

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19
Q

What is a vector equation?

A

An equation in which both sides of the equation are vectors of equal magnitude and direction

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20
Q

What is deceleration?

A

The rate at which an object decreases in velocity

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21
Q

Describe the displacement-time graph of an object with a constant velocity

A
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22
Q

Describe the displacement-time graph of an object with 0 velocity

A
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23
Q

Describe the displacement-time graph of an accelerating object

A
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24
Q

Describe the displacement-time graph of a decelerating object

A
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25
Q

What is the gradient on a displacement-time graph?

A

The velocity

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26
Q

What is the gradient on a displacement-time graph?

A

The velocity

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27
Q

What are graphs of motion?

A

Visual representations of the motion of a body

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28
Q

Draw the velocity-time graph for an object with a constant acceleration

A
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29
Q

Draw the velocity-time graph for an object moving at a constant velocity

A
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30
Q

Draw the velocity-time graph for a stationary object

A
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31
Q

Draw the velocity-time graph for an object with an increasing acceleration

A
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32
Q

How do you find the displacement using a velocity-time graph?

A

Find the area under the graph

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33
Q

What is the gradient of a velocity-time graph?

A

The acceleration

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34
Q

What does the area under an acceleration time graph represent?

A

The change in velocity

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35
Q

Determine the time at which car P overtakes car Q

A

8.25 seconds

36
Q

What is the equation for acceleration?

A

acceleration = Δvelocity/Δtime

37
Q

Draw the displacement time graph for a bouncing ball

A
38
Q

Draw the velocity time graph for a bouncing ball

A
39
Q

Draw the acceleration time graph for a bouncing ball

A
40
Q

What does SUVAT stand for?

A

S - Displacement
U - Initial velocity
V - Final velocity
A - Acceleration
T - Time

41
Q

What are the 5 SUVAT equations?

A
  • v = u + at
  • s = ½(u+v)t
  • v² = u² + 2as
  • s = ut + ½at²
  • s = vt - ½at²
42
Q

Which SUVAT equation does not contain s?

A

v = u + at

43
Q

Which SUVAT equation does not contain a?

A

s = ½(u+v)t

44
Q

Which SUVAT equation does not contain t?

A

v² = u² + 2as

45
Q

Which SUVAT equation does not contain v?

A

s = ut + ½at²

46
Q

Which SUVAT equation does not contain U?

A

s = vt - ½at²

47
Q

How is the SUVAT equation “v = u + at” derived?

A

a = Δv / Δt
a = (v-u) / t
at = v-u
v= u + at

48
Q

How is the SUVAT equation “s = ut + ½at²” derived?

A

s = ut + ½(v-u)t
s = ut + ½(at)t
s = ut + ½at²

49
Q

How is the SUVAT equation “s = ½(u+v)t” derived?

A

Start with s = ut + ½at²

s = ut + ½at²
s = ut + ½((v-u)/t)t² (substitute a = (v-u)/t)
s = ut + ½(v-u)t
s = ut + ½vt - ½ut
s = ½vt + ½ut
s = ½(v + u)t

50
Q

How is the SUVAT equation “v² = u² + 2as” derived?

A

Start with s = ½(v + u)t

s = ½(v + u)t
s = ½(v + u)(v - u)/a (substitute t = (v-u)/a)
2as = (v + u)(v - u)
2as = v² - vu + vu - u²
2as = v² - u²
v² = u² + 2as

51
Q

What is the most important SUVAT equation and why?

A

v = u + at as all the other equations can be derived from it

52
Q

What are the steps for solving a SUVAT equation question?

A
  1. State positive and negative directions
  2. Write out SUVAT and state your values
  3. Write out the required equation
  4. Solve
53
Q

Describe the motion of a skydiver as they jump out of the plane and open their parachute:

A

At the start of the jump, the air resistance is small and so the skydiver accelerates downwards at 9.81ms⁻². As his velocity increases, his air resistance will increase, causing acceleration to decrease. Eventually the air resistance will be big enough the balance the weight of the skydiver. Therefore the forces on the skydiver are balanced and so he stops accelerating and the velocity remains constant, this is his terminal velocity. When he opens his parachute the air resistance suddenly increases, causing him rapidly decelerate (slow down), as the upward force of air resistance is greater than the downward force of weight. Because he is slowing down the air resistance will decrease until it again balances the weight. At this point the skydiver has reached a new, lower, terminal velocity

54
Q

Draw the velocity time graph of a skydiver jumping out of plane and opening their parachute on earth and on the moon:

A

Blue = Earth
Red = Moon

55
Q

Explain the velocity time graph of a skydiver jumping out of plane and opening their parachute

Blue = on Earth
Red = on The Moon

A

On Earth:
At the start of the jump, the air resistance is small and so the skydiver accelerates downwards at 9.81ms⁻². As his velocity increases, his air resistance will increase, causing acceleration to decrease. Eventually the air resistance will be big enough the balance the weight of the skydiver. Therefore the forces on the skydiver are balanced and so he stops accelerating and the velocity remains constant, this is his terminal velocity. When he opens his parachute the air resistance suddenly increases, causing him rapidly decelerate (slow down), as the upward force of air resistance is greater than the downward force of weight. Because he is slowing down the air resistance will decrease until it again balances the weight. At this point the skydiver has reached a new, lower, terminal velocity

On the moon:
As the skydiver jumps, they will accelerate towards the ground at a constant rate (1.62 ms⁻²), this acceleration will not change as the skydivers velocity increases or when they open the parachute as there is no atmosphere on the moon, and therefore no air resistance. The acceleration is constant until they collide with the ground

56
Q

How is air resistance usualy treated in calculations?

A

It is ignored and treated as negligable, therefore SUVAT equations (which require constant acceleration) can be used for objects in freefall

57
Q

what is g?

A

The value of the gravitational field strength on earth (9.81ms⁻²)

58
Q

What is free fall?

A

An object is said to be in free fall when it is accelerating under gravity with no other force acting on it

59
Q

What is the acceleration of free fall denoted by?

A

g

60
Q

What are 3 methods for determining g?

A
  • Using an electromagnet and a trapdoor
  • Using light gates
  • Timing a ball dropping
61
Q

What is the equation for upthrust?

A

Upthrust = ρVg
Where, ρ = density of the liquid
V = volume of object submerged

62
Q

What are the forces acting on an object fully submerged in water?

A

Upward - Upthrust and Viscous Drag (water resistance)
Downwards - Weight

63
Q

What is Viscous Drag?

A

The friction between the fluid and a surface which may be the outside of an object or inside

64
Q

What is stopping distance?

A

Stopping distance is how long a vehicle will travel between the moment the driver sees the danger, and when the vehicle comes to a complete stop. Stopping distance = thinking distance + braking distance.

65
Q

What factors affect thinking distance?

A
  • Level of alertness
  • Drugs/alcohol in system
  • Distractions in/out of vehicle
  • Speed of Vehicle
66
Q

What factors affect braking distance?

A
  • Mass of vehicle
  • Condition of vehicle brakes
  • Condition of vehicle tyres
  • State of the road (gravel/ice/snow/rain)
  • Speed of vehicle
67
Q

What factor affects both braking distance and thinking distance?

A

Speed of vehicle

68
Q

That is the relationship between thinking distance and speed?

A

Thinking Distance ∝ Speed

69
Q

What is the realtionship between braking distance and speed?

A

Braking Distance ∝ Speed²

70
Q

Prove that: Thinking Distance ∝ Speed

A

Distance = Speed x Time
Work Done = Force x Distance

Work Done = Force x Speed x Time
Energy Transferred (to bring car to stop) = Force x Speed x Time

Energy Transferred (to bring car to stop) ∝ Speed
Thinking Distance ∝ Speed

71
Q

Prove that: Braking Distance ∝ Speed²

A

Kinetic Energy = ½ x Mass x Velocity²
Kinetic Energy = Energy Transferred (to bring car to stop)

Energy Transferred (to bring car to stop) = ½ x Mass x Velocity²

Energy Transferred (to bring car to stop) ∝ Speed²
Braking Distance ∝ Speed²

72
Q

For a particular car, the braking force is 70% of the weight of the car, show that the braking distance of the car travelling at a speed v, is given by: Braking Distance = 0.073v²

A

Braking Force = 0.7 Weight
0.7 Weight = 0.7mg

Kinetic Energy = ½ x Mass x Velocity²
Work Done = Force x Distance

Force x Distance = ½ x Mass x Velocity²
0.7mgd = ½mv²
0.7 x 9.81d = ½v²
d = 0.73

73
Q

What is thinking distance?

A

The distance travelled between the moment when the driver first sees a reason to stop, to the moment when the driver applies the breaks

74
Q

What is braking distance?

A

The distance travelled from the moemnt the brake is applied until the vehicle stops

75
Q

What is the equation for thinking distance?

A

Thinking Distance = Reaction Time x Speed

76
Q

What assumptions are made when calculating with projectile motion?

A

We assume horizontal motion is not slowed by air resistance, therefore there is no horizontal acceleration or deceleration

77
Q

How do you solve a projectile motion question?

A
  1. Draw a diagram
  2. Define the positive direction
  3. List what you have in the horizontal direction
  4. List what you have in the vertical direction
  5. Split question into vertical and horizontal components
  6. Calculate
78
Q

What is the same of the horizontal and vertical components when calculating projectile motion?

A

Time

79
Q

A projectile is launched at an angle of 45° to the horizontal with a velocity of 30 m/s. Calculate the maximum height reached by the ball and the horizontal distance at this height

A

Vertical = 22.9m
Horizontal = 45.9m

80
Q

A projectile is launched from the ground at an angle of 30° to the horizontal with a velocity of 20m/s. Calculate the horizontal distance it travels before it hits the ground again

A

35.3m

81
Q

A tennis ball is hit horizontally from the top of a building, it takes 4s to reach the ground and lands 80m form the building. What is:
* The height of the building?
* The vertical velocity of the ball just before it hits the ground?
* The horizontal Velocity?
* The resultant velocity and the angle it makes with the ground?

A
  • 78.5m
  • -39.2m/s
  • 20m/s
  • 44m/s, 63° to the horizontal
82
Q

Why is there no horizontal accleration for a projectile (assuming air resistance is negligable)?

A

The only force acting upon the object is weight, and since weight has a horizontal component of 0 there is no horizontal acceleration

83
Q

Explain how a systematic error in each of the measured quantities could have an affect on the gradient of the line

A
  • If there is a systematic error in “s”, there would be no change to the gradient as all points would be increased or decreased by the same amount
  • A systematic error in “t” would cause a change in the gradient as although the error in t is constant, “t^2” causes an increased error for each point therefore the gradient changes
84
Q

Explain how the time it takes for the ball to travel from A to B compares with the time it takes the ball to travel from B to C

A

The time is the same as for both the vertical distance and vertical acceleration are the same, therefore the time is the same

85
Q
A

0.75k

A Level Physics (29 decks)

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