hard questions Flashcards
define acceleration
change in velocity per unit time
explain one other way in which the air leaving the condenser is different
from the air entering the condenser
air is drier leaving because water vapour condenses
unit for impulse or momentum
Ns
The lid is removed from the bottle.
State and explain how the air pressure inside the bottle changes.
volume increases, air moves out of bottle, pressure decreases, until equal to pressure outside of bottle
Suggest why a Bluetooth headset only works well over short distances
radio waves lose energy get weaker with distance
Describe the mass and energy changes that take place during this process in a nuclear reactor. (nuclear fission)
nucleus converted into two smaller nuclei, smaller total mass, as converted into kinetic energy, energy increases
Describe how thermal energy from nuclear reactions is used to generate electricity in a power station.
(thermal energy-achieved from geothermal, nuclear reactions or heat from sun, or burning fossil fuels) used to heat / boil (cold) water OR make steam
* steam is at high pressure
* steam drives a turbine
* turbine (connected to and) drives a generatordue to its store of ke formed from spinning
* this turns coil of wire inside generator, moves a coil in a magnetic field producing electricity
* After the steam has spun the turbine, it is cooled in a condenser and re-enters the boiler system as water to be used again.
A protostar becomes a stable star when
inward force caused by gravitational attraction, is balanced equal to outward force caused by high temp of core
explain deacceleration
negative acceleration, decreasing velocity per unit time, rate of change in velocity
suggest one reason why a car wont start decelerating in 0 sec
thinking (reaction time) car will continue to travel at initial speed
why is deacceleration of the car greater than force over mass
air resistence acts in opposite direction to motion
why is the deacceleration of the car not constant
air resistence drag decreases with decreasing speed
resistive force changes
slow speed= bigger drag
state the form of energy stored in the water reservoir used to generate energy
gravitational
water flows to the turbine through a pipe of constant corss sectional area, explain why ke of water in the pipe remains constant as it flows through pipe
as cross sectional area is constant, volume is constant to ke= 1/2 mvˆ2, speed doesnt change as velocity and mass is constant, no changes made to pressure because temperature and area is constant
explain in terms of molecules how evaporation cools water in cloth
molecule with most ke escape surface of liquid/ cloth, molecules left have less avergae ke, cooling down temp in cloth, as they move slower. Ke is porportional to temp, thus temperature falls with decreasing ke
a sound wave has frequency of 1.5 MHz state and explain what type of sound wave it is
ultrasound, frequency above 20000 hz, above audible range
explain in terms of forces and motion of air molecules the cause of the motion of smoke particles
smoke particles constantly hit by small fast moving light air molecules, moving randomly, they exert a force due to change in momentum thus smoke particles appear to be moving in random directions in addition the smoke particles are larger heavier and slower.
state two ways in which transverse waves differ from longitudinal
transeverse waves are made up of crests and peaks, longitudinal made up of compressions and rarefractions
particles on a transverse wave ossillate perpindicular to wave direction/ energy propagation
typical speed of sound in water
1200 m/s- 1500 m/s
state one difference between emf and p.d
e.m.f= chemical to electrical energy
p.d= electrical to heat energy
state and explain which feature in a speed time graph shows acceleration
gradinet= rise/ run = change in speed/ change in time
state and explain acceleration in speed time graph where line is horizontal to x axis
acceleration= 0 because gradient= 0
suggest how does a train ahving a streamlined shape help to travel in high speed
decreases amount of air resistence it experiences
train took 80s to reduce speed from 84-42 m/s explain why with same braking force train takes more than 80s to reduce speed from 42 to zero m/s
slower the speed= less air resistence it experiences, meaning less force helping to slow train down= more time taken to slow it down