ODU(part 2)

Question 1

What is a projectile

Answer 1

A projectile is any object which freely accelerates due to gravity whilst moving forward at the same time.

Question 2

What are the 2 main types of projectiles

Answer 2

horizontal and angled

Question 3

What 2 componenets are projectiles made up of

Answer 3

projectiles are made up of horizontal and vertical components which act independently.

Question 4

Describe the horizontal component of a projectile

Answer 4

Constant velocity, no acceleration

Question 5

Describe the vertical component of a projectile

Answer 5

constant downwards acceleration due to gravity, where a = 9.8 ms^-2

Question 6

What is the formula for the horizontal component of velocity in an angled projectile

Answer 6

uh = ucos0

uh = initial horizontal speed
0 = angle of projectile
u = initial speed of projectile

Question 7

What is the formula for the vertical component of velocity in an angled projectile

Answer 7

Uv = usin0

uv = initial vertical velocity
0 = angle of projectile
u = initial speed of projectile

Question 8

The moon is a …

Answer 8

natural satellite

Question 9

The ISS is an…

Answer 9

artificial satellite

Question 10

What does gravitiation force between two objects depend on

Answer 10

the two masses

distance between their centres

Question 11

State newtons law of gravitation

Answer 11

F = Gm1m2/r^2

m1 and m2 are masses of the two objects in kg
r is the distance between the centres of the objects.
G is the universal constant of gravitation.

Question 12

State the universal constant of gravitation

Answer 12

G = 6.67*10^-11 Nm^2kg^-2 (given on data sheet)

Question 13

the gravitational force between an object and a planet is its []

Answer 13

weight

Question 14

What is a frame of reference

Answer 14

How you describe the motion of an object depends on how you observe it

Question 15

What is an inertial reference frame

Answer 15

Simply two places that are moving at constant speeds relative to one another.

Question 16

What is an absolute reference frame

Answer 16

A unique, universal frame of reference from which everything could be defined or measured. Einstein proved no such reference frame exists.

Question 17

What are einsteins 2 postulates (assumptions)

Answer 17

1) observers moving at constant speed relative to one another (inertial frames) will observe the same laws of physics.

2) the speed of light in a vacuum is the same for all observers regardless of their motion relative to the light source.

Question 18

What is time dilation

Answer 18

Time dilation is the difference in a time interval as measured by a stationary observer and a moving observer.

Question 19

State the dilated time formula

Answer 19

t’ = t/ (√(1-(v/c)^2))

where t is proper time
t’ is dilated time
v is the velocity of the object relative to a rest frame
c is the speed of light in a vacuum

Question 20

Define proper time

Answer 20

Proper time is the time measured in the frame in which the clock is at rest relative to the event. The time will always be shorter in the rest frame.

Question 21

Define dilated time

Answer 21

Dilated time is the time measured on a clock that is moving with a constant velocity relative to you. The time will be longer so the clock is seen to be running slow.

Question 22

What is length contraction

Answer 22

Length contraction is a difference in the length of an object as measured (parallel to the direction of travel) by a stationary observer and a moving observer.

Question 23

What is the formula for length contraction

Answer 23

l’ = l(√(1-(v/c)^2))

Question 24

Define proper length

Answer 24

Length measured by the observer at rest with respect to the moving object

Question 25

Define contracted length

Answer 25

Contracted length of the object as measured by another observer.

Question 26

What is the lorentz factor

Answer 26

The lorentz factor is a way of taking into account the speed of a moving object.

Question 27

State the lorentz factor

Answer 27

Y = 1/(√(1-(v/c)^2))

Question 28

At what point relative to c are relativistic effect neglible at

Answer 28

Relativistic effects are neglegible when speed are below about 0.1c

Question 29

At what speed relative to c does length contraction become significant

Answer 29

0.8c

Question 30

Dilated time is measured by

Answer 30

an observer who is not in the frame of reference that the event is taking place.

Question 31

Length contraction only occurs in

Answer 31

the direction parallel to the motion.

Question 32

What is the doppler effect

Answer 32

The doppler effect is the change in observed frequency when a sound source is moving relative to a stationary observer

Question 33

What happens when a sound source is moving towards a stationary observer

Answer 33

more waves reach you per second so the frequency of the sound is increased (wavelength is decreased)

Question 34

What happens when a sound source is moving away from a stationary observer

Answer 34

Less waves reach you per second so the frequency of the sound is decreased (wavelength is increased)

Question 35

State the doppler equation

Answer 35

fo = fs(v/(v+/-vs) where v is the velocity of sound fo is frequency heard by the observer fs is the frequency emmited by the source vs is of the moving source

Question 36

State 2 applications of the doppler effect

Answer 36

Ultrasound in medicine Radar speed guns

Question 37

Define redshift

Answer 37

When a lightsource is moving away from you, the frequency decreases, so the spectrum shifts to longer wavelengths. This is called redshift.This is the doppler effect applied to light.

Question 38

State the redshift formula

Answer 38

z = (λo - λr)/ λr where z is redshift (no units) λo is the observed wavelength in metres λr is the rest wavelength in metres

Question 39

z is positive for _______ and negative for _________

Answer 39

Redshift, Blueshift

Question 40

State the formula for redshift provided that stars and galaxies are moving at non relativistic speeds

Answer 40

z = v/c where: z is redshift with no units v is recessional velocity of the star in metres per second c is the speed of light in metres per second

Question 41

What were Hubbles two conclusions (Hubble Lemaitre's law)

Answer 41

1) The bigger the magnitude of the shift the greater the speed the galaxy was moving away from the earth. 2) The further away a galaxy is the greater the speed it is travelling

Question 42

State 2 things known about the expansion of the universe

Answer 42

The galaxies do not expand (they are gavitationally bound) Space between the galaxies expands carrying the galaxies with it.

Question 43

State the hubble lemaitre's law formula

Answer 43

V = Hod where: Ho is hubbles constant with units per second d is distance to the galaxy from earth in metres, m v is the recessional velocity of the galaxy in metres per second

Question 44

Plotting a graph of recessional velocity of galaxies against their distnace from earth gives a straight line of best fit through the origin, the gradient of this graph gives....

Answer 44

the value for hubbles constant.

Question 45

State hubbles constant

Answer 45

2.3x10^-18 s^-1

Question 46

Explain how the age of the universe can be found using hubbles law

Answer 46

Hubbles law suggests that galaxies further away from us are moving away faster than galaxies closer to us. Therefore the universe is expanding If we asusume the rate of expansion is fixed then most galaxies have been moving apart at a constant rate. So time taken for them to reach their relative positions (ie age of the universe) must be t = d/v Since Ho = v/d, then the age of the universe = 1/Ho = 4.35x10^17 s

Question 47

What is dark matter and how do we know it exists

Answer 47

We can determine the mass of galaxies from their orbital speed, but the total masses measured are bigger than the mass accounted for by the observable stars in a galaxy. The unaccounted mass is called dark matter.

Question 48

Why is the universe still expanding despite the existence of dark matter, what is opposing the additional gravitational effects caused by the increase of matter

Answer 48

Dark energy

Question 49

Define dark energy

Answer 49

Dark energy is a source of energy capable of producing a force which acts against the gravitational force of attraction, pushing matter apart.

Question 50

Ordinary matter and energy make up what % of the universe

Answer 50

4%

Question 51

Dark energy makes up what % of the universe

Answer 51

74%

Question 52

Dark matter makes up what % of the universe

Answer 52

22%

Question 53

A hot star will appear what colours

Answer 53

blue ish

Question 54

A cooler star will appear what colour

Answer 54

reddish

Question 55

How does peak wavelength relate with temperature

Answer 55

Peak wavelength is shorter for hotter objects than for cooler objects

Question 56

How does radiation relate with temperature of objects

Answer 56

Hotter objects emmit more radiation per units surface area per unit time than cooler objects.