EXAM - Questions to Memorise Flashcards
State and explain the angle which will produce the maximum range as the launch height increases
launch angle becomes less then 45
Explain terminal velocity
Terminal velocity occurs acceleration due to gravity is canceled out by the area resistance making the net force on an object 0.
Air resistance increases with velocity.
When parachuter deploys their parachute their velocity decreases and thus the air resistance slowly increase until a new terminal velocity is reached.
Describe and explain the effects of air resistance on:
- vertical and horizontal components
- max height
- range
Vertical component:
slowed on way up and down (takes longer to fall from max height to ground)
Horizontal - deccelerates
Max Height - decreases max height (same flight time)
Range - Decreases range with sudden drop
Explain why Newton’s Law of Universal Gravitation is consistent with Newton’s third law of motion.
Newton’s 3rd Law states that the objects exert equal sized but oppositely directed forces as each other.
As the gravitational force on each star is proportional to the product of their two masses, the magnitude of force on both stars must be the same.
As gravitational force is attractive, the forces on the stars must be in opposite directions (towards the other star).
Hence, the gravitational force between the stars is consistent with Newton’s 3rd Law.
Explain why an object travelling in a circular path accelerate even though it has a constant speed.
As the direction of the object is constantly changing, its velocity is changing. As acceleration involves a change in velocity the object is therefore accelerating.
OR There’s a net force always perpendicular to the velocity. According to Newton’s 2nd Law, this force results in an acceleration.
Use one of Kepler’s Laws to explain why comets in highly elliptical orbits are only seen once in a large number of years, and when they are seen, they are only observed for a short period of time.
From Kepler’s 1st Law, the sun is at one focus of the comet’s elliptical orbit. As the orbit it highly elliptical, the comet passes close to the sun and turns again a large distance from the sun. It takes the comet a long time to travel the large distance to the far point of the orbit.
According to Kepler’s 2nd Law, the area swept per unit time is equal at all points along the orbit path. Hence, when the comet is close to the sun, it is traveling very fast and it only seen for a short time.
Explain how particles formed in the upper atmosphere are able to be detected, despite having short decay times.
Since particles formed in the upper atmosphere are moving at high speeds from the frame of reference of a stationary observer on Earth, time is dilated and moves slower for the particles. Therefore, in their frame of reference they only move a short distance, an observer on Earth will measure a significantly larger time period before it decays, and hence a greater distance is travelled. The means the particles can travel longer distances and be detected on Earth.
Explain why it is impossible to accelerate an object to he speed of light, even if it has a continuous force acting upon it.
As an object approached the speed of light, the kinetic energy approaches infinity. For an object to reach the speed of light, the work done on the object too would approach infinity. Since it is impossible to do an infinite amount of work on a mass, it is impossible to reach the speed of light.
Describe the path followed by an electron in a uniform electric field (with positive plate on the top)
The path followed by the electron is parabolic and towards the positive plate. This is because the electric force acting on it is constant in magnitude and direction (upwards towards positive plate). This force causes the vertical velocity to change; whilst its horizontal velocity remains constant thus causing parabolic motion.
Describe how Lenz’s Law is consistent with the Law of Conservation of Energy
Lenz’s Law states that an induced emf created by a change in magnetic flux, creates an induced current which opposes the change in magnetic flux producing the emf.
According to the Law of Conservation of Energy, energy cannot be created or destroyed.
The work done in overcoming the opposing force that is produced when a change in magnetic flux occurs is converted to electrical energy.
Describe the relationship between the oscillating electric and magnetic field and the direction of travel of an EM wave
The electric and magnetic fields oscillate perpendicular to each other and perpendicular to the direction of travel of the wave.
Give one reason why light from an incandescent source is not coherent
It does not give off waves with a constant phase relationship between them as the many charges in the hot filament oscillate randomly in both phase and frequency.
State one safety precaution that should be taken when using a laser
ONE of the following:
- Do not darken the room in which you are using the laser
- Do not place your eye or others in the path of the laser beam
- Do not shine the laser onto reflective surfaces
Derive fmax = ev/h
Work done by the electric field in accelerating the electrons is equal to the gain in kinetic energy of the electrons
TF, eV = K
Max frequency occurs when an electrons loss all it energy to a single photon.
Ep = hfmax
TF, eV = hfmax
fmax = eV/h
Sketch a labeled graph of a typical spectrum produced by an x-ray tube.
Also state how the maximum frequency will change if he tube current is increased.
Reaches a peak intensity
characteristic peaks
f-max when intensity is 0
Tube current will not change fmax
