Perfect Answers (according to the SQA) From: http://www.mrsphysics.co.uk/higher/perfect-answers-according-to-the-sqa/

Terminal Velocity

A constant velocity of an object when the driving force acting on an object is balanced by the frictional force.

Resultant force

A single force that has the same effect as the forces actually acting on an object

Spectral lines

A 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.

scalar and vector

A vector is a quantity which has both a magnitude and direction. A scalar is fully described by its magnitude.

acceleration

Acceleration is the rate of change of velocity

Explain, 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

Satellites a curved path

Constant horizontal speed but are accelerating in the vertical direction under the influence of a gravitational field.

Radiation 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".

Big Bang Evidence

Cosmic Microwave Background Radiation, Redshift of galaxies, Olber's Paradox (and darkness of the skies), H-He Problem (relative abundance of hydrogen/helium)

Collisions- law of conservation of momentum

During 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.

Explain 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

inertia

Inertia is the tendency of a body to remain at rest, or if moving, to continue its motion in a straight line

Redshift explanation

Light from objects moving away is shifted to larger wavelength or the rate of change of wavelength/emitted wavelength as the galaxy moves away

Lorenz transformation not noted at low speeds.

Lorentz factor is (approximately) unity/equal to one negligible change in length/time/mass observed

Redshift example

More distant galaxies are moving away at a greater velocity/ have a greater recessional velocity

Newton- definition

One Newton is equal to the force which causes an acceleration of one metre per second squared when applied to a mass of one kilogram.

Redshift, z

Redshift, 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.

twin paradox

Special 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.

F-t graphs

The Area under a F-t graph is equal to impulse or change in momentum of the object.

Doppler Effect

The Doppler Effect is the apparent change in frequency of a wave when the source and observer are moving relative to each other.

Big Bang Description

The Universe was initially in a hot and very dense state and then rapidly expanded. The universe started from a point/singularity and rapidly expanded.

Reference Frame

The background frame against which measurements are made. There is no absolute reference frame.

Length contraction

The 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.

Explain 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

Explain 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.

Open Universe

The universe will continue to expand forever.

Closed universe

The universe will slow its expansion and eventually begin to contract.

acceleration of X ms-2

The velocity of the body increases/changes by X m s-1 every second.

Doppler explanation

There are more wavefronts per second observed due to the forward motion of the vehicle. (NB not wavefronts produced as there are not!)

impulse

This quantity Ft is called the IMPULSE and it is equal to the CHANGE IN MOMENTUM of the object. Impulse = change in momentum

Air bags / crumple zones / seat belts

Time (of collision) increased, change in momentum is the same, (Average) force (acting on passenger) is decreased/reduced/smaller

Time dilation

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

Law of conservation of momentum

Total momentum before (a collision) is equal to the total momentum after (a collision) in the absence of external forces

Component of weight down a slope

W sin θ, or mg sin θ

Dark Energy

a 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.

Dark Matter

a hypothetical form of matter invisible to electromagnetic radiation, postulated (suggested) to account for gravitational forces observed in the universe. Dark Matter is attractive

Cosmic Microwave Background Radiation. CMB Give a reason why the existence of this radiation supports the Big Bang Theory.

is 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.

momentum

the product of mass times velocity

Hubble Constant Ho and 1/Ho

the 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.

inertial reference frame

two objects that are moving at constant speed with reference to each other