Physics 1010 exam 1
The brakes of a 1500−kg car exert a force of 3 kN. How long will it take for them to slow the car to a stop from an initial speed of 29 m/s?
*1 kN = 1000 N
density of water
1 gram/cm^3
1 joule =
1 kg m2 / s2
Unit conversions
1 mile = 1.61 kilometers 1 gallon = 3.79 liters 1 pound = 2.2 kilograms 1 Km = 1000 m 100 cm = 1 m 1 in. = 2.54 cm 1 m = 3.28 ft
Kinetic theory
1. Gas molecules are small and far apart 2. Gas molecules undergo elastic collisions 3. Gas molecules are non-interacting
The energy problem
1. Increasing demand for energy 2. Decline in supply of fossil fuels (81% of worlds energy) 3. Environmental concerns - CO2
velocity
d/t+ direction
density of water x volume displaced =
density of object x volume of object
Mass
density x volume
Friction
direction of this force always opposes the motion
Kinetic energy
directly proportional to the mass of the object and to the square of its velocity. KE = 1/2mv^2
velocity =
distance / time
phase changes
during a phase change energy is either consumed or released. Increasing energy from solid to liquid to gas to plasma
second law of thermodynamics
entropy cannot decrease (entropy = a measure of disorder)
Change in velocity
final velocity - initial velocity - can change by speeding up or slowing dow, or changing direction
action reaction theorem
forces occur in pairs
Air resistance during free fall
friction during free fall means net force is reduced, objects gain speed as they fall Resistance increases with speed, friction force becomes equal to gravity
Work =
fxd
Vector quantity
have direction and magnitude (size). ex. velocity
Heat flows from
higher temperature to lower temperature
accuracy
how close the measure is to the true value
Newton's third law
if one object exerts a force on a second one, then the second object exerts an equal but opposite reaction force
When the kinetic energy of an object is doubled (mass remaining constant), the momentum...
increases by about 40% (by 2, or 1.41 times). KE will be 2KE, and since mass can't be changed, the velocity must change.
centripetal force
inwards - what makes circular motion possible - proportional to the square of the velocity of the object and inversely proportional to the radius of a curved path Fc = mv^2/r Unit: N
Mass SI unit
kg
Energy unit
kilowatt/hr
volume
lwh, m^3
Velocity/speed
m/s - meters per second
force
mass x acceleration (ma) - measured in newtons (N) = kgm/s^2 1 kN = 1000 N
density (P = rho)
mass/volume, kg/m^2. this is an intrinsic property of an object that stays the same
power
measure of the rate at which work is accomplished work(or energy)/time (j/s)
Einstein's theory of relativity
measurements are relative and depend on which frame of reference you're using
work done against gravity
mgh
Buoyancy
net upwards pressure on any object immersed in a liquid
Inertial reference frame
no acceleration in this frame
Elastic collision
objects are not deformed after. Ex. Bouncy ball. energy is conserved.
scalar quantity
only contains info about magnitude. familiar scalar quantities include Temperature, power, mass
centrifugal
outwards
Ellipse
ovular shaped - the sum of the distances from 2 foci is constant for planets, the sun is at one foci
Linear momentum (denoted by P) equation
p = m x v.
Charle's law + Boyle's law --> Ideal gas law
pV/t = constant
Energy equation
power x time
Temperature
proportional to average kinetic energy of molecules that make up a substance
Energy=
pt
speed
rate of change of a position - does not contain directional information (scalar quantity)
Variable sources of energy
rate of energy production varies with the time of day ex. solar, tidal, wind, waves
precision
repeatability of the measurement using the same instrument
Same temperature =
same thermal energy
time unit
seconds
Motion of the earth around the sun
slower when farther away, faster when closer
Thermal expansion
solids expand as particles vibrate faster at higher temperatures
Heat
sum of the kinetic energy of all of the particles that make up a body
Retrograde motion
the apparent motion of a planet in a direction opposite to that of other bodies within its system, as observed from a particular vantage point.
most important convective heating
the atmosphere
Radiation
the emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles that cause ionization.
velocity of a falling object is directly proportional to
the length of time the object has been falling
Convection
the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat. - fluids
conduction
the process by which heat or electricity is directly transmitted through a substance when there is a difference of temperature or of electrical potential between adjoining regions, without movement of the material. - Solids, molecular heat
Kepler's 3rd law
the ratio between the square of the time needed by a planet to make a revolution around the sun and the cube of its average distance from the sun is the same for all the planets. Te2/Re3 = Ta2/Ra3 Where Te = distance of earth from the sun (1AU) and Re=The distance of the earth from the sun
net force
the sum of all forces acting on an object
Source of all energy on earth
the sun
most important radiative head transfer
the sun! All objects radiate and absorb energy at all times. If there is more energy absorbed than given off, temperature goes up - pupils and dark surfaces
Heat engines
turns heat into mechanical energy by bringing a working substance from a higher state temperature to a lower state temperature.
Direction of the acceleration of swing of a pendulum at the midpoint?
upwards
Distance
v x t (speed x time) - meters (m)
Time =
v/g
Momentum can be 0 only if..
velocity is 0
acceleration due to gravity is always...
vertically downwards
power is measured in
watts
Buoyant force
weight of fluid displaced by a body - does not depend on the weight of the object - only on the weight of the displaced fluid = mass of displaced water x gravity = density of water x volume displaced x gravity weight = mg
terminal velocity
when air resistance equals gravitational force and they cancel out - net force = 0
insulator
wood, cork, air, snow
vertical velocity
√2gh
height
1/2gt^2
gravitational potential energy
1/mgh
Two tugboats are towing a ship. Each exerts a horizontal force of 3 tons and the angle between their towropes is 90°. What net force is exerted on the ship?
4.2. Pythagorean theorem
Big G Constant - Gravitational constant
6.67 x 10^-11 N
How many square feet are there in an area of 7.8 square meters?
84.2 ft^2 - 1 m = 3.28 ft. 1m^2 = 3.28^2 = 10.8 ft. 7.8 x 10.8 = 84.2
little g
9.8 m/s^2, this is a constant - every second, velocity is changing by 9.8
Kepler's 2nd law
A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time
vector quantities are often represented by...
A straight line with an arrowhead The length of the line yields information about MAGNITUDE The arrow indicates the DIRECTION
Newton's law of gravitational force
ALL objects attract each other with a force of gravitational attraction. This force of gravitational attraction is directly dependent upon the masses of both objects and inversely proportional to the square of the distance that separates their centers. - Force of gravity is proportional to mass 1 + mass 2 / distance between centers
If the polar ice caps melt, the length of the day will increase. Why?
According to the Law of Conservation of Angular Momentum, if the level of the sea rises, the earth's spin on its axis will slow down.
Fossil fuels
All carbon based - petroleum products, coal, natural gas - rich in chemical potential energy - nonrenewable
Pressure facts
At a given depth, throughout a static connected fluid, pressure stays the same. Pressure increases the deeper you go
charles law
At constant pressure, and far from liquefaction, all gases have the same expansion coefficient. AKA volume of gas changes if temperature does - warm air expands - convection
Direction of acceleration in pendulum swing halfway down from the furthest point towards the midpoint?
At some angle to the path, pointing above the path
An object at rest can have.. A. Non-zero KE b. non zero gpe c. non zero momentum d. non zero velocity
B. Non-zero GPE. At rest object has no velocity. No velocity means no anything associated with velocity
Carbon capture and storage
CO2 emissions from coal burning facilities are captured and pumped via pipeline deep into the earth
Kepler's 1st law
Elliptical foci - planetary orbits are ellipses with the Sun at one focus of the ellipse
Universal law of gravity
F = m1 x m2 / distance^2 x G
Law of conservation of momentum
For a collision occurring between object 1 and object 2 in an isolated system, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision. Momentum can be exchanged.
When falling...
GPE decreases. Kinetic energy increases. Together there is no change. The change occurs when the object hits the ground.
Ptolemy
Geocentric model
How does a nuclear power plant produce electricity?
Heat from nuclear fissions in the reactor produces steam that drives turbines connected to electric generators.
Copernicus
Heliocentric model
Energy is measured in
Joules
Momentum is greatest where..
Kinetic energy is greatest because this is where velocity is the greatest
The north star - polaris
Looks stationary relative to other stars for observers on Earth since it is aligned with the Earth's axis of rotation
Best thermal conductors
Lots of electrons - gold, silver, copper
Where is KE greatest on a pendulum?
Lowest point the bottom (max at lowest point, min at highest)
Angular momentum
Momentum associated with the rotation of a body about some axis. The direction of this momentum is parallel to the axis of rotation
Right now, you are sitting perfectly still in your seat what is the NET FORCE being exerted on your body?
NET force = 0 The force down from gravity and the force up from the chair cancel out!
What must be your location if the stars move across the sky in circles centered directly overhead?
North or South Poles
Pressure
Pascals - 1 kP = 1000 p. Pressure = force over constant area a = f/a. Smaller area? More pressure
The diagram shows a planet orbiting the sun. Where is the planet's angular momentum the greatest?
Same everywhere - Angular momentum is conserved because there is no external torque on the system
The acceleration of gravity on the surface of Venus is 8.9 m/s2. What would happen to a ball thrown upward on Venus compared to one thrown upward with the same speed on Earth? (Atmospheric resistance is neglected).
T = total time of flight = 22h / g. Since g is smaller on Venus than Earth, T will be greater and the ball will return to the ground later on Venus.
Newton's second law
The acceleration of any object is directly proportional to the net force on the object and inversely proportional to its mass. a=f/m
If the moon were half as far from the earth as it is today, how would the gravitational force it exerts on the earth compare with the force it exerts today?
The force would be four times what it is today.
The earth takes almost exactly 24 h to make a complete turn on its axis, so we might expect each high tide to occur 12 h after the one before. However, the actual time between high tides is 12 h 25 min. What can account for this?
The moon is moving relative to the earth, changing the times of high and low tides by 50 minutes in 24 hours.
In terms of what you would actually observe, what does it mean to say that the moon apparently moves eastward among the stars?
The moon's position will move eastward of any reference star when observed on consecutive nights.
Special relativity
The moving object at constant velocity with no acceleration - inertial reference frame
First postulate of theory of relativity
The speed of light is constant
Kepler's third law
The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
A year corresponds to the time it takes for an observer on the earth to see.....
The sun migrate eastward completely around the sky
Inelastic collision
There is deformation after the collision. Energy is not conserved - it dissipates into other forms
If the Earth had no Moon then what would happen to the tides?
There would be small but noticeable tides and they would occur less often
Newton's first law
When no net force is acting on an object, an object at rest will remain at rest and an object in motion will remain in motion
Nuclear fission
Where nuclear energy comes from - the breaking apart or decomposition of large nuclei - usually uranium
The length of day has varied. When did the longest day thus far occur?
Yesterday, because the day's length has been increasing steadily for 380 million years
rate
a change in any quantity proportional to time
motion
a change in position
why do we have two high tides in a day?
a. the earth moon gravitational force b. the earth is not spinning on its central axis. water is pushed outwards as it rotates due to centrifugal force`
Change in speed is calculated by
acceleration x time. final speed = initial speed + change in speed
Acceleration to gravity only...
acts in the VERTICAL direction
calorie
amount of energy needed to raise the temperature of one kg of water by 1ºC
Specific heat
amount of heat needed to raise the temperature of 1 kg of water by 1º celsius: Q=mc∆t
Archimedes principle
an immersed body experiences an upward force equal to the weight of the fluid displaced by the body.
Boyle's law
at constant temperature, pressure x volume is constant. P1/p2 = v2/v1 - compressed gas has higher pressure
constant acceleration
can calculate this if we know final and initial velocity and acceleration.
Continuous energy source
can supply energy continuously ex. hydroelectric, geothermal
converting celsius to Fahrenheit
celsius x (9/5) + 32
acceleration
change in velocity/time. Occurs when there is a change in speed or direction. Common units: m/s^2, ft/s^2, mph^2
Gasification
coal transformed into a mixture of gases - syngas - can be used in methane production (which is cheap and renewable)
You are driving your car and approaching a stop sign. You apply the brakes when your speedometer reads 27 m/s (60 mph). If you know that the breaks will provide an acceleration of a = - 6m/s2, how far away must you apply the brakes?
d = v1t + 1/2at^2