Transcript TAKS Objective 5 - Net Start Class

TAKS Objective 5
Energy, Motion, Waves
and
Energy Changes
Physics is the study of energy and
provides answers to our energy needs:
• Mechanical energy to do work such as grind
wheat or churn milk into cheese saves fossil
fuels and electricity and can be produced by
wind.
• Using solar energy to produce heat or hot water
also saves on generating electricity.
Let’s see if you are ready . . .
• Answer the next 7 questions, if you do so
without error, you are probably ready for
Objective 5 TAKS.
• If you miss one, go to the slide # given to
review that material.
• If you miss more than one, be sure to
review each of those sections.
1. The typical automobile’s kinetic energy is
converted to heat energy when the brakes are
applied. A braking system that converts kinetic
energy to electrical energy instead of heat energy
has been designed. The electrical energy can be
used later to move the car again. How does a
system like this benefit the environment?
F Greater use of solar energy
G Ability to harness wind energy
H Decreased use of fossil fuels
J Use of renewable hydroelectricity
2. Why is the sum of the products’ energy in this reaction
less than the sum of the reactants’ energy?
A Energy is trapped in the reactants.
B The products absorb available energy.
C Energy is given off as heat.
D The reactants’ energy is less than the melting point of
glucose
2.0 m
5.0 m
3. What is the approximate
difference in gravitational
potential energy of the
two shaded boxes?
A 79 J
B 59 J
C 39 J
D 19 J
4. A 1-kilogram ball has a kinetic energy of
50 joules. The velocity of the ball is —
F 50 m/s
G 25 m/s
H 10 m/s
J 5 m/s
5.
A 0.50 kg ball with a speed of 4.0 m/s
strikes a stationary 1.0 kg target. If
momentum is conserved, what is the total
momentum of the ball and target after the
collision?
A 0.0 kgm/s
B 0.5 kgm/s
C 1.0 kgm/s
D 2.0 kgm/s
6. The picture above shows the directions in which
water leaves this scallop’s shell. Which picture
below shows the direction the scallop will move?
• Which of the following waves would
have the highest pitch and lowest
volume?
A
B
C
D
Check your answers.
1.
2.
3.
4.
H: Cars usually run on gasoline, so any heat energy
saved, reduces use of fossil fuels.
C: This is the equation for cellular respiration and
the “lost energy” is often used as body heat.
B: Calculate PE for each and subtract.
H: KE=½(mv2) so 50= ½(1 x v2) or
100 = v2.
5.
6.
7.
Momentum = mass x velocity or 5.5 x 100 or 550 kg
m/s.
D: For each action an equal opposite reaction, since
the force is out and down, the shell will move up.
B: This wave has the greatest frequency which
determines pitch (more waves in the same time) and
is the shortest, which is lowest amplitude so lowest
volume.
Energy
Is defined as
the ability to
do work
Energy has two
Kinetic
(Energy
of
Motion)
types:
and
Potential (Stored Energy)
Law of Conservation of Energy
• Energy can change forms, but is never
created nor destroyed
• Loss in one form = gain in an another form
Potential Energy
2 possibilities
Gravitational PE Object lifted to a
height
Elastic PE - A
stretched or
compressed object
(spring or rubber
band)
Elastic Potential Energy
5 According to the data in the
table, about how far can a
spring be expected to
stretch when a force of
3.92 N is applied?
A 10.5 cm
B 13.6 cm
C 14.0 cm Although this question is about reading the
D 17.3 cm table, it does show that a stretched spring can
do work (force x distance). Look at the
numbers, as Force increases by 0.98, the
distance doubles, so the answer would be:
Gravitational Potential Energy
PE = mgh
41 What is the
potential energy
of the rock?
m = 95joules
kg
A 59,900
2
g
=
9.8
m/s
B 64,600 joules
h = 100
m
C 93,100
joules
95 kg x 9.8 m/s2 x 100
D 121,600 joules
=93,100 joules C
Kinetic Energy
KE = m
2
v
2
Ex: The man is doing
work, using kinetic
energy.
Weight= Mass (m) X gravity (g)
•
•
•
•
Weight Unit of mass = kg
gravity = 9.8 m/s/s
Unit of weight = Newton
1 Newton= about ¼
pound
On Earth gravity = 9.8 m/s/s
For every second that
an object falls it
accelerates 9.8 m/s
each second.
A maximum speed is
reached when the air
resistance (friction)
slowing the object
increases to prevent
further acceleration.
This is called terminal
velocity.
Universal Law of Gravitation
All objects in the universe
attract each other by the
force of gravity
Gravity varies depending on
two factors:
1) the mass of the object
doing the pulling, and
2) the distance from the
center of that object
46 Which of these would cause the
gravitational force between Earth
and the sun to decrease?
F An increase in the length of a day
on Earth
G An increase in the distance
between Earth and the sun
H An increase in the number of
planets orbiting the sun
J An increase in the masses of
Earth and the sun
What are the 2 factors that effect gravity?
Distance and Mass; decrease distance,
increases gravity. increase mass,
increase gravity. . . .
Energy Conversion
• Changing from one type of
energy to another is the
basis of all machines, and
life processes on earth.
• Our main energy use,
electricity is converted from
mechanical energy, nuclear
energy or chemical energy.
• During conversions, some of
the energy is converted to
heat by friction so it is not a
100% efficient process.
Motion can be described as
• a change in an
object’s position.
• Average speed is the
change of position
(distance) of an
object over time
• If speed also has a
direction it is called
velocity.
Definition of a Force
• A Force is a push or a pull
Velocity Graphs V = distance
time
Pink,
Which line, pink or
blue has the greatest
velocity?
Distance (m)
• Velocity (v) is steeper
the slope (rise slope!
over run) of a
60
distance (d) vs.
40
time (t) graph
Velocity
Series1
Series2
20
0
1 3 5 7 9 11 13 15
Time (sec)
40 The diagram represents the total travel of a
teacher on a Saturday. Which part of the trip is
made at the greatest average speed?
FQ
How do we work this one?
GR
Calculate v = d/t for each segment.
HS
J T
4 The picture shows the position of a ball
every 0.25 second on a photogram. Using a
ruler, determine the velocity of the ball.
Use the ruler on the side of the chart to measure from
the front of ball 1 to the front of ball 2 and multiply by 4
(since the pictures are at ¼ seconds). OR front of ball 1
to the front of ball 3, and multiply by 2 since two
pictures would be ½ a second. V = d/t
Acceleration is a change in an
object’s velocity over time
• When an object’s
speed changes over
time it is accelerating
(or decelerating)
• A = vfinal – vinitial
time
• Units for acceleration
m/s/s or m/s2
Acceleration Graphs
Acceleration
Velocity ((m/s)(m)
• Acceleration (a) is
the slope of a
velocity (v) vs. time
(t) graph
• When plotted on a
distance vs. time
graph, acceleration
is an exponential
curve (J curve)
60
40
20
0
1
3
5
7
9
11
Time (sec)
13
15
Read the graph first, what is each
segment telling you?
In
first second?
41the
According
to this
graph,
During
thewhat
nextwas
4 the
bicycle’s
acceleration
seconds,
from
1 to 5 or
6 seconds?
between 6 and 10
seconds?
What
about between 610
seconds?
A 0.0
m/s2
Between
102and 12.5
B 0.65 m/s
seconds? 2
C 1.6 m/s
What
D 6.5about
m/s2 12.5 to 15
seconds?
Balanced Forces
• A force that
produces no
change in an
object’s motion is
balanced by an
equal, opposite
force.
F=ma,
the mass
40kg
and the acceleration
Remember
to is
read
diagrams
first! What is
3.0m/s
– 0.0m/s
divided
by 1.2s.
Soread
it is the
40kg x
happened
in the
pictures?
Now
2.5m/s/s or 100N
question . . .
32 Starting from rest at the center of a skating
rink, two skaters push off from each other over a
time period of 1.2 s. What is the force of the
push by the smaller skater? ANSWER
F 16 N
G 32 N
H 88 N
J 100 N
Friction
A force that acts to oppose
motion. It occurs between any
two surfaces in contact with
each other, or as air resistance.
Friction
Friction causes an
object to slow down
and stop.
Since the amount of
energy stays
constant, the energy
becomes heat.
To reduce friction oil
or other lubricants
are used.
44 A wet bar of soap slides 1 meter across a
wet tile floor without appearing to slow down.
Which of these statements explains why the
bar of soap fails to slow down?
F A constant force on an
object produces a constant
positive acceleration.
G An object in motion tends
to remain in motion in the
absence of an external
force.
H A moving object having
constant velocity contains
kinetic energy.
J An object’s weight is
proportional to its mass.
This is an example
of how a lubricant
works, reducing
friction so the
inertia keeps the
soap moving.
Momentum = Mass x Velocity
• The larger the mass OR the faster an object
moves, the more momentum it has. That means
it will hit harder, or do more damage.
• If a penny is thrown it probably won’t hurt very
much, but if it is shot from a sling shot with a
higher velocity, it will hurt a lot!
27 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
Formula Page says that
Momentum = Mass x Velocity
D 0.5 kg
So 15 kg.m/s = M x 30 m/s
solving for M it is:
Newton’s 1st Law of
Motion
• Objects in motion
stay in motion
• And objects at rest
stay at rest
• Until they are
acted upon by an
unbalanced force.
Newton’s 2nd
Law of Motion
The greater the force applied
to an object, the greater it
will accelerate.
Force = Mass X Acceleration
or F=ma
Newton’s 3rd Law of Motion
• For every
action force
there is an
equal and
opposite
reaction
force.
20 How many Newtons of force does a 70.0 kg
deer exert on the ground because of gravity?
Record and bubble in your answer on the
answer document.
• This is an example of
a weight problem
since the weight is the
force is due to gravity.
• F = mg or
= 70kg x 9.8m/s/s
= 686 Newtons
18 What is the net force exerted on a 90.0
kg race-car driver while the race car is
accelerating from 0 to 44.7 m/s in 4.50 s?
F 9.8 N
G 20 N
F = ma, where
H 201 N
m= 90.0kg
J 894 N
a = (44.7 – 0)/ 4.5s
So, the answer is:
Okay, let’s try again. . .
• Answer the next 5 slides.
• Check your answers at the end. Don’t
cheat and look first. You aren’t helping
yourself!!
• If you get them correct, Great you can
move on to the next physics section –
1 When the air is released from a balloon, the air
moves in one direction, and the balloon moves
in another direction. Which statement does this
situation best illustrate?
F What goes up must come down.
G For every action there is an equal and
opposite reaction.
H The shape and size of an object affect air
resistance.
J The acceleration due to Earth’s gravity is 9.8
m/s2.
2. Assuming the chart
contains all energy
transformations in
the Earth system,
how much solar
radiation goes
toward evaporating
water?
F 133,410 terajoules
G121,410 terajoules
H 92,410 terajoules
J 40,000 terajoules
3. A catapult was designed to project a small metal ball at a
target. The resulting data are shown in the table. Which of
these might explain the difference between the calculated
and actual distances?
A The ball landed short of the calculated distance because of
an increase in momentum.
B Air resistance caused the ball to land short of the calculated
distance.
C Initial mass of the ball changed with each trial.
D The metal ball was too small for accurate measurements to
be made.
4. The table contains data for two wrecking balls
being used to demolish a building. What is the
difference in momentum between the two
wrecking balls?
F 300 kgm/s
G 200 kgm/s
H 150 kgm/s
J 0 kgm/s
Car velocity = 5.5m/s
Car velocity = 0m/s
Car velocity = 0m/s
Driver velocity = 5.5m/s Driver velocity = 5.5m/s Driver velocity = 0m/s
Driver mass = 100kg
Driver mass = 100 kg
Driver mass = 100 kg
5. 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 the crash-test dummy’s momentum is
absorbed by the air bag? Record and bubble in
your answer to the nearest whole number on the
answer document. (Just write it down)
6. As you step off of the water raft ride
at 6 Flags over Texas, you notice
that the boat moves away from the
pier when you try to step towards
the pier. This is explained by which
of Newton’s laws?
a. Newton’s First Law
b. Newton’s Second Law
c. Newton’s Third Law
7. Which of Newton’s laws would apply
to the following situation?
25 N
a. Newton’s First Law
b. Newton’s Second Law
c. Newton’s Third Law
25 N
8. As a log burns in the fireplace, the
energy conversion taking place is
from _____.
a. Kinetic energy to radiant energy
b. Kinetic energy to potential energy
c. Potential energy to thermal energy
d. Thermal energy to potential energy
9. Diagram 1 represents a wave. Diagram 2 represents the
composite wave formed when a second wave interferes
with the original wave. Which of the following best
represents the second wave?
10. The sound heard by the person in
front of the car in the picture would
hear a sound whose pitch is _____.
a. the same as the actual pitch
b. higher than the actual pitch
c. lower than the actual pitch
Check your answers!
1. G
2. J
3. B
4. J
5. 550 kg*m/s
6. C
7. C
8. C
9. A
10. B