Transcript TAKS Physics Review (Objective 5)

TAKS Review - Formulas
Integrated Physics and Chemistry (4) Science Concepts.
The student knows concepts of force and motion evident in
everyday life. The student is expected to:
(A) calculate speed, momentum, acceleration, work, and
power in systems such as in the human body,
moving toys, and machines;
Common measurements and
symbols
Measurement
Symbol
Typical Units on TAKS
speed or velocity
v
m/s
momentum
p
kg.m/s
acceleration
a
m/s2
Work
W
J
Power
p
W
Force
F
N
Time
t
s
Mass
m
kg
E, KE or PE
J
Energy
Using the formula chart
1. Circle what you are asked to find
2. Underline given facts with numbers and units
and write the symbol above it.
3. Identify the formula(s) you will use from the
formula chart
4. Rearrange the formula for what you’re asked to
find.
5. Put in numbers for symbols and solve.
6. Check that you answered the question asked.
Rearranging formulas
When a formula is not solved for the variable
you are trying to find, then you need to
rearrange it until your variable is alone on
one side of the equation.
Rearranging formulas
Example, the speed formula is:
If you are given speed and time and want to
find distance, what would the formula be?
Rearranging formulas
Here, you divided d by t. To
move t to the other side, do
the opposite, multiply by it.
t cancels on the right side
And you are left with the
formula for d.
Speed and Velocity
How fast an object is traveling.
Velocity has direction, speed does not.
Acceleration
The change in velocity
Can be:
• speeding up
• slowing down
• or changing direction
If an object is moving at a constant speed,
acceleration = 0
Negative acceleration (deceleration) means the
object is slowing down.
Work
Using force to move an object a certain
distance.
If there is no movement, there is no work
done. If distance = 0, work = 0
The displacement must be in the direction of
the force.
Does not depend on the time it takes to do
the work
If Distance = 0,
then
Work = 0.
The man is carrying his groceries 2 meters
to the counter. He is holding the groceries
with a force of 10 N, what is the work done
on the groceries?
The force and the displacement are not
in the same direction. Therefore,
Distance = 0,
Work = 0.
If the man had been lifting the
groceries up, then there would be work.
Power
The rate at which work is done.
More power means the same work can be
done faster.
How could this person increase his
power?
What is the power of this motor?
Power = Work/time
Time = 5 s
We must find the work first!
Work = Force x distance
= 10 N x 2m = 20 J
Power = Work/time
= 20J/5s
=4 Watts
Momentum
The product of an object’s mass and
velocity.
Can be thought of as how difficult it is to stop
a moving object.
A stopped object has zero momentum.
Conservation of Momentum
In collisions, total momentum does not
change. The momentum of the objects
(together) before the collision is the same
as the momentum of the objects (together)
after the collision.
Distance vs. Time graphs
• In a distance vs. time graph, the slope of
the line is the speed of the object.
• If you have a horizontal line, the object is
stopped.
Distance (Miles)
25
20
No speed = stopped
15
10
5
0
0
5
Tim e (hours)
10
120
100
100
Distance (Miles)
Distance (Miles)
120
80
60
40
80
60
40
20
20
0
0
0
5
10
Tim e (hours)
Constant speed away from a point
0
5
10
Tim e (hours)
Constant speed toward a point
100
Distance (Miles)
Distance (Miles)
200
150
100
50
80
60
40
20
0
0
0
0
5
10
5
10
Tim e (hours)
Tim e (hours)
The line gets steeper – speeding up
The line gets less steep – slowing down
Velocity vs. Time Graphs
• In a velocity vs. time graph, the slope of
the line is the acceleration of the object.
• In this type of graph, a horizontal line
means that the object is moving at a
constant speed.
• 1. A ball moving at 30 m/s has a
momentum of 15 kg·m/s. The mass of the
ball is —
A 45 kg
B 15 kg
C 2.0 kg
D 0.5 kg
• 2. The weight lifter used a force of 980 N
to raise the barbell over her head in 5.21
seconds. Approximately how much work
did she do in raising the barbell?
F 380 J
G 982 J
H 2,000 J
J 10,000 J
3. How much work is performed when a 50
kg crate is pushed 15 m with a force of
20N?
F 300 J
G 750 J
H 1,000 J
J 15,000 J
4. According to this graph, what was the
bicycle’s acceleration between 6 and 10
seconds?
A 0.0 m/s2
B 0.65 m/s2
C 1.6 m/s2
D 6.5 m/s2
5. If a force of 100 newtons was exerted on
an object and no work was done, the
object must have —
A accelerated rapidly
B remained motionless
C decreased its velocity
D gained momentum
6. A mechanic used a hydraulic lift to raise a
12,054 N car 1.89 m above the floor of a
garage. It took 4.75 s to raise the car.
What was the power output of the lift?
A 489 W
B 1815 W
C 4796 W
D 30,294 W
7.
• 9.The pictures show how an air bag functions in
a collision. How much momentum in kg.m/s
does the air bag absorb from the crash-test
dummy if all of the crash-test dummy’s
momentum is absorbed by the air bag?
P = m x v = 100 kg x 6.3 m/s = 630 kg x m/s
Integrated Physics and Chemistry (4) Science
Concepts.
The student knows concepts of force and motion evident in
everyday life. The student is expected to:
(B) Investigate and describe [applications of] Newton’s laws
such as in vehicle restraints, sports activities, geological
processes, and satellite orbits.
Forces
• Force can be defined as a push or a pull.
• Forces can be balanced, which mean they
are equal and opposite with no change in
direction. If the forces on an object are
balanced, it will either remain at rest or it
will move at a constant speed in a straight
line.
Unbalanced forces cause an object to
accelerate (speed up, slow down or
change direction) in the direction of the
largest force.
Friction is a force that acts in the opposite
direction to the motion of a moving object.
Newton’s Laws
Newton’s First Law: An object at rest will
remain at rest and an object in motion will
remain in motion at a constant velocity
unless acted upon by an unbalanced
force.
• The Law of Inertia.
Orbits and Inertia
Newton’s Second Law:
• Force = mass x acceleration
• For a constant force, if mass increases
acceleration decreases
• For a constant mass, if force increases,
acceleration increases
The force on the ball and the force on the cannon are equal
(See 3rd Law).
F = ma
The ball’s mass is lower, so its acceleration is higher.
The cannon’s mass is greater, so its acceleration is lower.
Newton’s Third Law: For every
action force, there is an equal
and opposite reaction force.
1. Which of these is the best description of
the action- reaction force pair when the
space shuttle lifts off from the launchpad?
A The ground pushes the rocket up while exhaust
gases push down on the ground.
B Exhaust gases push down on air while the air pushes
up on the rocket.
C The rocket pushes exhaust gases down while the
exhaust gases push the rocket up.
D Gravity pulls the rocket exhaust down while friction
pushes up against the atmosphere.
2. After shooting a cannonball, a
cannon recoils with a much lower
velocity than the cannonball. This is
primarily because, compared to the
cannonball, the cannon has a —
F much greater mass
G smaller amount of momentum
H greater kinetic energy
J smaller force applied to it
3. How many newtons of force
does a 50.0 kg deer exert on the
ground because of gravity?
F=mxa
50 kg x 9.8m/s2 = 490 N
4. Which factor would most likely
cause a communications satellite
orbiting Earth to return to Earth from
its orbit?
F An increase in the satellite’s
forward momentum
G An increase in solar energy striking
the satellite
H A decrease in the satellite’s size
J A decrease in the satellite’s
velocity
TAKS Review: Simple machines
(D) investigate and demonstrate [mechanical
advantage and] efficiency of various
machines such as levers, motors, wheels and
axles, pulleys, and ramps. (11th only)
Simple machines
Simple machines are tools that
make work easier, usually do work
with a single movement
Simple machines
The amount of effort saved when
using machines is called mechanical
advantage or MA
Mechanical Advantage
Mechanical advantage is how many times a
machine multiplies the force that is put into it.
For example, if you put in a force of 10 N, and
the machine puts out a force of 40 N, then the
machine has multiplied your force ___ times.
The mechanical advantage is 4.
(Remember Work remains the same!)
Mechanical advantage is calculated
by the following formula:
MA =
Resistance force= Fr
Effort force
Fe
For example, if a worker applies a force of
20 N to pry out a nail that has a resistance
force of 500N, what is the mechanical
advantage of the hammer the worker
uses?
MA = Resistance force
Effort force
= 25
= Fr =
Fe
500 N=
20 N
Ideal MA
If you do not know the forces applied, the
mechanical advantage a machine should
provide (called ideal MA) can be
calculated by the following formula:
IMA = Effort distance
Resistance distance
Pulleys
The mechanical advantage of a pulley = the
number of supporting strings. If you pull
up on a string you count it. If you pull
down on a string you don’t count it.
What is the MA?
3
2
4
Levers
In a lever, the MA can be found by dividing
the distance between the fulcrum and the
effort by the distance between the fulcrum
and resistance.
Levers
So, to make a lever easier to use, move the
fulcrum closer to the weight you are trying
to move and further from where you are
pushing.
Which is easiest to move?
Ramp
To increase the MA of a ramp (to make the
ramp easier to climb), make the ramp
longer with a more gradual incline.
How could you make this ramp
easier to climb?
Wheel and axle
• To increase the MA of a wheel and axle,
make the wheel larger and the axle
smaller.
A gear system is a modified type of wheel and
axle, where the larger gear acts as the wheel
and the smaller gear acts like the axle. How
could you change these gears to make the
smaller one turn faster?
Make the larger gear
larger or the smaller gear
smaller.
Efficiency
• If a machine were perfect, all of the work
that was put in would be used to do useful
work.
• In real life, some work put into a machine
is “lost” as heat or friction.
• We calculate efficiency to determine how
much of the work put in actually produces
useful work.
Efficiency
• Efficiency = Work out x 100%
Work in
• If a machine were perfect and there were
no friction, efficiency would be 100%,
because all of the work in would become
work that came out.
• In real life, efficiency is always less than
100%!!!!
The diagram shows an electric motor
lifting a 6 N block a distance of 3 m. The
total amount of electrical energy used by the
motor is 30 J. How much energy does the
motor convert to heat?
F 9J
G 12 J
H 18 J
J 21 J
Which lever arrangement requires the least
effort force to raise a 500 N resistance?
What is the efficiency of an air
conditioner if there is a work input
of 320 J and a work output of 80 J?
F 4%
G 25%
H 240%
J 400%
Which configuration of pulleys and
belts shown below will result in the
fastest rotation of Spindle 2?
Integrated Physics and Chemistry (6)
Science Concepts.
The student knows the impact of energy
transformations in everyday life. The
student is expected to
(A) describe the law of conservation of
energy.
Energy
• energy- the ability to do work
• unit: joule (J)
Types of Energy:
– kinetic energy- the energy of motion
• the faster an object moves, the more kinetic energy
KE = ½ (mv2)
– potential energy- energy of position
• stored energy – ex: a ball rolled to the top of a hill
• GPE is potential energy due to gravity. GPE = mgh
(remember g = 9.8m/s2)
law of conservation of energy• energy may neither be created nor
destroyed
• it can only be transformed into various forms—
from kinetic to potential, from chemical to
mechanical
• the total energy in the system is constant
Where is the PE greatest?
Where is the PE least?
Where is the KE greatest?
Where is the roller coaster moving
the fastest?
Types of Energy
mechanical energy- Moving objects
heat energy- usually results from friction—causes
phase & temperature changes
chemical energy- stored in chemical bond bonds
Example, released when starting a fire, burning fuel,
digesting food
nuclear energy- Nuclear reactions; produces the sun’s
energy due to nuclear fusion--hydrogen changes to
helium
electromagnetic energy- Charges—microwaves, Xrays, light
Energy conversions
Energy conversions
Powerful Plankton
The U.S. Naval Research Laboratory has created an experimental marine fuel
cell that could produce enough electricity to power ocean-monitoring devices.
This fuel cell runs on seawater and sediment, with the help of plankton. Some
plankton on the surface of ocean sediments use dissolved oxygen to break
down organic matter, releasing energy; this is an aerobic process. The
plankton in the deeper sediments break down organic matter without using
oxygen; this is an anaerobic process. These two processes create a
difference in voltage between the surface of the sediment and the sediment
farther down in the seabed. The voltage difference can be used to produce
electricity-up to 5.0 x 10 – 2 watts of power. Energy supplied by this type of
fuel cell can be obtained as long as there is organic matter in the sediment.
Fuel cells powered by plankton from the seabed can be used to operate
instruments that monitor ocean currents and water temperature. These fuel
cells get their energy by converting —
F chemical energy to electrical energy
G electrical energy to mechanical energy
H hydroelectric energy to geothermal energy
J mechanical energy to chemical energy
Which process best shows the
conversion of solar energy to
chemical energy?
F Prevailing winds causing windmills to spin
G Green plants making their own food
H Uranium producing heat to make steam
J Tides generating electricity
What is the potential energy of the rock?
A 59,900 joules
B 64,600 joules
C 93,100 joules
D 121,600 joules
Which of the following is an
example of solar energy being
converted into chemical energy?
F Plants producing sugar during the day
G Water evaporating and condensing in the
water cycle
H The sun unevenly heating Earth’s surface
J Lava erupting from volcanoes for many
days
An inventor claims to have created an
internal combustion engine that converts
100 kJ of chemical energy from diesel fuel
to 140 kJ of mechanical energy. This claim
violates the law of conservation of —
F momentum
G inertia
H energy
J mass
Integrated Physics and Chemistry (6) Science Concepts.
The student knows the impact of energy transformations in everyday life.
The student is expected to
(B) investigate and demonstrate the movement of heat through solids,
liquids, and gases by
convection, conduction, and radiation
Remember the properties of solids,
liquids and gases…
• heat- energy caused by the internal
motion of molecules
• heat transfer- the movement of heat from
a warmer object to a cooler one
3 methods of heat transfer
1. conduction- heat transferred by direct
contact of molecules
• takes place in solids, liquids, & gases, but does
best in solids
• one particle must contact another for this to occur.
In solids, the particles are close to each other,
which makes contact easier.
Conductors vs. Insulators
conductors- substances that
conduct heat better & more rapidly
than others (silver, copper, iron)
insulators- substances that do not
conduct heat easily (glass, plastic,
wood, rubber)—wearing several
layers of clothing in extremely cold
weather
3 Methods of Heat Transfer
2. convection- takes place in liquids &
gases as up-and-down movements called
convection currents.
• Important: Does not occur in solids
Convection – look for arrows or
circular motion
3 Methods of Heat Transfer
3. radiation- heat energy transfer through
empty space
• This is how the sun heats the earth
Which method is shown?
Radiation
Conduction
Which method is shown?
Convection
Radiation/ Convection
Radiation
Convection/
Conduction
Conduction
The primary way liquids and gases transmit
heat is by the process of —
A reflection
B conduction
C radiation
D convection
A man who was sleeping wakes up because
he hears the smoke alarm go off in his
house. Before opening the bedroom door,
the man feels the door to see whether it is
warm. He is assuming that heat would be
transferred through the door by
Conduction
_________________________
A solar heater uses energy from the sun to
heat water. The heater’s panel is painted
black to —
F improve emission of infrared radiation
G reduce the heat loss by convection
currents
H improve absorption of infrared radiation
J reduce the heater’s conducting properties
In which container is the substance unable
to transfer heat by convection?
Container P and Container Q each were filled with 0.5
liter of water. The water was heated to 90°C. The
table shows the temperatures after both containers
were allowed to cool for 3 minutes. Compared to
Container Q, Container P is a better
A conductor
C radiator
B absorber
D insulator
TAKS Review: Waves
The student knows the effects of waves on everyday life. The student is
expected to
(A) demonstrate wave types and their characteristics through a variety of
activities such as modeling with ropes and coils, activating tuning forks, and
interpreting data on seismic waves. (10th only)
(B) demonstrate wave interactions including interference, polarization,
reflection, refraction, and resonance within various materials. (11th only)
Types of Waves
1. Transverse
2. Longitudinal (compression)
Parts of a Wave
Calculating Wave Speed
Speed = Wavelength • Frequency
Measured in Hz
Interference
Constructive
Destructive
Reflection
Angle of incidence = Angle of reflection
Refraction
Refraction is the
bending of light
as it passes from
one medium to
another.
Refraction
Pencil appears bent
in a glass of water.
Spear fishing: the
fish is actually
lower than it
appears to be.
Refraction
A prism separates
white light into its
components
Diffraction
When a wave meets an obstacle it bends around the
obstacle.
Resonance
Resonance occurs when two nearby objects
share the same vibrational frequency.
When one of the objects is vibrating, it
forces the second object into vibrating.
The result is a large vibration = a large
sound (in sound waves)
Resonance
Example: Two similar tuning forks.
When one tuning fork is sounded, the
second tuning fork is energized by the specific
frequencies emitted by the first, and begins to
vibrate and sound as well!
Other examples of resonance:
• Plucked strings on musical instruments
(guitar)
• Air blown across a tube (flute) or bottle of
water
• Vocal cords
Polarization
At 0°C sound travels through air at a
speed of 330 m/s. If a sound wave is
produced with a wavelength of 0.10 m,
what is the wave’s frequency?
F 0.0033 Hz
G 33 Hz
H 330 Hz
J 3300 Hz
• Which illustration best demonstrates
compression waves?
Which wave has the greatest
velocity?
When trying to spear a fish in water, a
person needs to take into account the way
light bends as it moves from water into air.
The bending of light as it passes from one
medium into another is known as —
F reflection
G refraction
H diffraction
J polarization
One tuning fork is struck and
placed next to an identical fork. The
two forks do not touch. The second
tuning fork starts to vibrate
because of —
F interference
G the Doppler effect
H resonance
J standing waves
The pitch of a sound made by
plucking a guitar string is
determined by the —
A frequency of the vibration
produced
B strength of the plucking force
C distance between the strings
D shape of the guitar body
The diagram shows waves
approaching a barrier.
Which pattern will be
formed after the waves
pass through the opening
in the barrier?
Electric Circuits
IPC 6F – Investigate and compare series and
parallel circuits. (10th grade only)
Circuits
To have an electric circuit, you need:
• a closed conducting path which extends
from the positive terminal to the negative
terminal.
• An energy source, such as a battery.
Will the bulb light?
Will the bulb light?
Closed
loop!
Series circuit
• each device is connected in a manner
such that there is only one pathway by
which charge can traverse the external
circuit.
What happens if the first
light bulb burns out?
Parallel Circuits
• multiple pathways by which charge can
flow through the external circuit.
What happens if the first
light bulb burns out?
Circuit Math
Voltage (Volts)
Current (Amps)
Resistance (Ώ)
Which switch, if opened, will cause the lightbulb to stop glowing?
FQ
GR
HS
JT
What is the current in a copper wire that has a
resistance of 2 ohms and is connected to a 9volt electrical source?
F 0.22 amp
G 4.5 amps
H 11.0 amps
J 18.0 amps
How much current is flowing through this
circuit?
A 0.32 A
B 3.1 A
C 4.0 A
D 12.5 A
Which circuit is built so that if one lightbulb goes out, the
other three lightbulbs will continue to glow?