Perfect Answers (according to the SQA)

I will add and adapt these as I go through the past papers. If you’ve got additional definitions do pass them on. These would be great written on cue or flash cards. Go through past papers and record any common phrases or answers.

perfect answers.xlsx

perfect answers.xlsx
1accelerationAcceleration is the rate of change of velocity
2acceleration of  X  ms-2The velocity of the body increases/changes by  X  m s-1 every second.
3Air bags / crumple zones / seat beltsTime (of collision) increased, change in momentum is the same, (Average) force (acting on passenger) is decreased/reduced/smaller
4Big Bang DescriptionThe Universe was initially in a hot and very dense state and then rapidly expanded. The universe started from a point/singularity and rapidly expanded.
5Big Bang EvidenceCosmic Microwave Background Radiation, Redshift of galaxies, Olber’s Paradox (and darkness of the skies), H-He Problem (relative abundance of hydrogen/helium)
6Closed universeThe universe will slow its expansion and eventually begin to contract.
7Collisions- law of conservation of momentumDuring any collision, in the absence of external forces momentum is conserved, total energy is conserved. In an elastic collision – Ek is also conserved In an inelastic collision- Ek is transferred into other forms.
8Component of weight down a slopeW sin θ, or mg sin θ
9Cosmic Microwave Background Radiation. CMB Give a reason why the existence of this radiation supports the Big Bang pervasive throughout space. It is the dominant source of radiation in the Universe. It is very uniform (throughout the Universe). It is isotropic (throughout the Universe). It shows the characteristics of blackbody radiation. It has a temperature of approx 3 K (2·74 K) due to cooling on expansion. It corresponds to a redshift of 1000, so the early temperature of this radiation was approx 3000 K. CMBR is thought to be the “afterglow” of the Big Bang, cooled to a faint whisper in the microwave region.
10Dark Energya hypothetical form of energy whose negative pressure counteracts gravity and is assumed to be responsible for the universe expanding at an accelerating rate. Dark Energy repels.
11Dark Mattera hypothetical form of matter invisible to electromagnetic radiation, postulated (suggested) to account for gravitational forces observed in the universe. Dark Matter is attractive
12Doppler EffectThe Doppler Effect is the apparent change in frequency of a wave when the source and observer are moving relative to each other.
13Doppler explanationThere are more wavefronts per second observed due to the forward motion of the vehicle. (NB not wavefronts produced as there are not!)
14Evidence for the big bangThe cooling of the Universe and cosmic microwave background radiation provide evidence for the Big Bang
15Explain why a greater number of muons are detected on the surface of the Earth than would be expected if relativistic effects were not taken into account.For an observer on Earth’s frame of reference the mean life of the muon is much greater OR The distance in the muon frame of reference is shorter
16Explain why star is redshifted.The star is moving away from the Earth • The apparent wavelength of the hydrogen spectra from the star has increased • The apparent frequency of the hydrogen spectra from the star is less than the actual frequency on Earth • The frequency of the light from the star has shifted towards the red end of the spectrum • Light from the star is experiencing a Doppler shift.
17Explain why the driving force must be increased with time to maintain a constant acceleration.The faster it goes, the greater the air resistance. or frictional forces / friction / drag then F(drive) constant, the unbalanced force would decrease or increasing F(drive) keeps the unbalanced force constant or overall/net force – must have
18Explain, in terms of the forces, why there is a maximum angle of slope that the cart can ascend.As angle (of slope) increases mgsinθ increases When mgsinθ ≧ engine force – friction, the vehicle cannot move up the slope
19F-t graphsThe Area under a F-t graph is equal to impulse or change in momentum of the object.
20Hubble Constant Ho and 1/Hothe ratio of the speed of recession of a galaxy (due to the expansion of the universe) to its distance from the observer. The reciprocal of the constant is called Hubble time and represents the length of time for which the universe has been expanding, and hence the age of the universe.
21impulseThis quantity Ft is called the IMPULSE and it is equal to the CHANGE IN MOMENTUM of the object. Impulse = change in momentum
22inertiaInertia is the tendency of a body to remain at rest, or if moving, to continue its motion in a straight line
23inertial reference frametwo objects that are moving at constant speed with reference to each other
24Law of conservation of momentumTotal momentum before (a collision) is equal to the total momentum after (a collision) in the absence of external forces
25Length contractionThe decrease in length (in the direction of motion) of an object moving relative to an observer. N.B. it must be clear that the observer is in a different frame of reference.
26Lorenz transformation not noted at low speeds.Lorentz factor is (approximately) unity/equal to one negligible change in length/time/mass observed
27momentumthe product of mass times velocity
28Newton- definitionOne Newton is equal to the force which causes an acceleration of one metre per second squared when applied to a mass of one kilogram.
29Open UniverseThe universe will continue to expand forever.
30Radiation of peak wavelength 1·06 mm can be detected on Earth coming from all directions in space.Cosmic Microwave Background All three words required (Radiation) “CMBR” – Not acceptable, as this is not “naming”.
31Redshift exampleMore distant galaxies are moving away at a greater velocity/ have a greater recessional velocity
32Redshift explanationLight from objects moving away is shifted to larger wavelength or the rate of change of wavelength/emitted wavelength as the galaxy moves away
33Redshift, zRedshift, z, of a galaxy is defined as the change in wavelength divided by the original wavelength, and given the symbol z. It has no units.
34Reference FrameThe background frame against which measurements are made. There is no absolute reference frame.
35Resultant forceA single force that has the same effect as the forces actually acting on an object
36Satellites a curved pathConstant horizontal speed but are accelerating in the vertical direction under the influence of a gravitational field.
37scalar and vectorA vector is a quantity which has both a magnitude and direction. A scalar is fully described by its magnitude.
38Spectral linesA spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range. Spectral lines are often used to identify atoms and molecules from their characteristic spectral lines. These “fingerprints” can be compared to the previously collected “fingerprints” of atoms and molecules, and are thus used to identify the atomic and molecular components of stars and planets.
39Terminal VelocityA constant velocity of an object when the driving force acting on an object is balanced by the frictional force.
40Time dilationTime dilation is a difference in a time interval as measured by a stationary observer and a moving observer.
41twin paradoxSpecial Relativity would suggest one twin who has been out in space or travelling at high speed relative to one remaining on Earth should come back younger, but to the travelling twin they could consider themselves stationary as the Earth moved away fast, so to the astronaut twin the twin on Earth should be younger. This paradox is resolved as during the journey in space the travelling twin would have had to return, during which time they would be in a non-inertial reference frame, so they would have experienced the speed/acceleration. Therefore been in a non inertial reference frame and hence special relativity does not apply.
42Speed of light is the same for all observers / all (inertial) frames of reference
43Correct – from the perspective of the stationary observer there will be time dilation Incorrect – from the perspective of the students they are in the same frame of reference as the clock Not possible to say/could be both correct and incorrect – frame of reference has not been defined
44light is redshifted/ shifted towards red

Proving the equations of motion

Equation 1

v u at

Equation 2

v-t graphs ut 12at2


Equation 3

EOM equation 3

If you don’t like proving v2=u2+2as from v=u+at then use this neat little sheet from Mr Mackenzie.

using displacement equation to prove the last equation

Below are the 16 graphs to try to learn. Going across a row from L to R shows graphs drawn from the gradient of the previous graph. Therefore if you write the axes on for s-t, v-t and a-t you can work backwards and forwards to quickly picture the shape of the graph you require.16graphs

Friction always acts to oppose motion. If the object is sliding down the slope then friction must act up the slope, but if the object is being pushed up the slope then friction acts down the slope.friction down slopefriction up slopeThe component pushing into the slope (mg cosθ) is balanced by the reaction force from the slope.



Collisions Seatbelts, crumple zones, airbags, helmets etc are all designed to reduce the force on a person, by increasing the time of contact. In all cases the change in momentum or impulse remains the same as the vehicle/ object still has to come to rest from its initial speed.lower force


finding g

Show that the frequency f of the sound heard by the passenger is given by where symbols have their usual meaning.Doppler proof

Although we talk about the Big Bang, it is important to emphasise that the universe, ie space, is expanding. There are a number of characteristics that indicate it is an expansion and not the result of an explosion.

Explosion Expansion
Different bits fly off at different speeds Expansion explains the large-scale symmetry we see in the distribution of galaxies
Fast parts overtake slow parts Expanding space explains the redshifts and the Hubble law
Difficult to imagine a suitable mechanism to produce the range of velocities from 100 kms–1 to almost the speed of light Expansion also explains redshifts and the Hubble law even if we are not at the centre of the universe


Type of Collision Momentum Kinetic Energy Total Energy
Elastic Conserved Conserved Conserved
Inelastic Conserved Reduced Conserved
Explosions Conserved

zero at start and finish

here Ep is converted to Ek so Ek increases Conserved

Hope these are helpful. Let me know if you want me to add anything further.