TAKS Objective 5

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TAKS Objective 5

• Energy, Motion, Waves
• and
• Energy Changes

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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.

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Lets 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.

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• 1. The typical automobiles 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

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• 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

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• 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

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• 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

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• 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

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• 6. The picture above shows the directions in
  which water leaves this scallops shell. Which
  picture below shows the direction the scallop
  will move?

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• Which of the following waves would have the
  highest pitch and lowest volume?

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Check your answers.

• 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 KE½(mv2) so 50 ½(1 x v2) or
• 100 v2.
• 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.

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Energy

• Is defined as the ability to do work
• Energy has two
• types

Kinetic (Energy of Motion) and Potential (Stored
Energy)
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Law of Conservation of Energy

• Energy can change forms, but is never created
  nor destroyed
• Loss in one form gain in an another form

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Potential Energy 2 possibilities

• Gravitational PE -Object lifted to a height
• Elastic PE - A stretched or compressed object
  (spring or rubber band)

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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
• D 17.3 cm

Although this question is about reading the
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
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Gravitational Potential Energy PE mgh

• 41 What is the potential energy of the rock?
• A 59,900 joules
• B 64,600 joules
• C 93,100 joules
• D 121,600 joules

m 95 kg g 9.8 m/s2 h 100 m 95 kg x
9.8 m/s2 x 100 93,100 joules C
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Kinetic Energy

• KE m v2
• 2
• Ex The man is doing work, using kinetic energy.
  

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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

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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.

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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

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• 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. . . .
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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.

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Motion can be described as

• a change in an objects position.
• Average speed is the change of position
  (distance) of an object over time
• If speed also has a direction it is called
  velocity.

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Definition of a Force

• A Force is a push or a pull

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Velocity Graphs V distance
time
Pink, steeper slope!

• Velocity (v) is the slope (rise over run) of a
  distance (d) vs. time (t) graph

Which line, pink or blue has the greatest
velocity?
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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? F Q G R H S J
T
How do we work this one? Calculate v d/t for
each segment.
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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
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Acceleration is a change in an objects velocity
over time

• When an objects speed changes over time it is
  accelerating (or decelerating)
• A vfinal vinitial
• time
• Units for acceleration m/s/s or m/s2

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Acceleration Graphs

• 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)

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Read the graph first, what is each segment
telling you?

• 41 According to this graph, what was the
  bicycles 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

In the first second? During the next 4 seconds,
from 1 to 5 or 6 seconds? What about between
6-10 seconds? Between 10 and 12.5 seconds?
What about 12.5 to 15 seconds?
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Balanced Forces

• A force that produces no change in an objects
  motion is balanced by an equal, opposite force.

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Remember to read diagrams first! What happened
in the pictures? Now read the question . . .
Fma, the mass is 40kg and the acceleration is
3.0m/s 0.0m/s divided by 1.2s. So it is 40kg x
2.5m/s/s or 100N

• 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?
• F 16 N G 32 N H 88 N J
  100 N

ANSWER
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Friction

• A force that acts to oppose motion. It occurs
  between any two surfaces in contact with each
  other, or as air resistance.

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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.

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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 objects weight is proportional to its mass.

This is an example of how a lubricant works,
reducing friction so the inertia keeps the soap
moving.
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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 wont hurt very
  much, but if it is shot from a sling shot with a
  higher velocity, it will hurt a lot!

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27 A ball moving at 30 m/s has a momentum of 15
kgm/s. The mass of the ball is

• A 45 kg
• B 15 kg
• C 2.0 kg
• D 0.5 kg

Formula Page says that Momentum Mass x Velocity
So 15 kg.m/s M x 30 m/s solving for M it
is
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Newtons 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.
  

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Newtons 2nd Law of Motion

• The greater the force applied to an object, the
  greater it will accelerate.
• Force Mass X Acceleration
• or Fma

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Newtons 3rd Law of Motion

• For every action force there is an equal and
  opposite reaction force.

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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

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• 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
• H 201 N
• J 894 N

F ma, where m 90.0kg a (44.7 0)/ 4.5s So,
the answer is
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Okay, lets try again. . .

• Answer the next 5 slides.
• Check your answers at the end. Dont cheat and
  look first. You arent helping yourself!!
• If you get them correct, Great you can move on to
  the next physics section

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• 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 Earths gravity is
  9.8 m/s2.

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• 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

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• 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.

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• 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

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Car velocity 5.5m/s Driver velocity 5.5m/s
Driver mass 100kg
Car velocity 0m/s Driver velocity
5.5m/s Driver mass 100 kg
Car velocity 0m/s Driver velocity 0m/s 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 dummys 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)

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• 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 Newtons
  laws?
• Newtons First Law
• Newtons Second Law
• Newtons Third Law

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• 7. Which of Newtons laws would apply to the
  following situation?
• Newtons First Law
• Newtons Second Law
• Newtons Third Law

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• 8. As a log burns in the fireplace, the energy
  conversion taking place is from _____.
• Kinetic energy to radiant energy
• Kinetic energy to potential energy
• Potential energy to thermal energy
• Thermal energy to potential energy

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• 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?

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• 10. The sound heard by the person in front of the
  car in the picture would hear a sound whose pitch
  is _____.
• the same as the actual pitch
• higher than the actual pitch
• lower than the actual pitch

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Check your answers!

1. G
2. J
3. B
4. J
5. 550 kgm/s
6. C
7. C
8. C
9. A
10. B