Review TAKS Physics

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ReviewTAKS Physics

• Motion• Motion can be described as change in position of

a body.• Average velocity (speed) is the change of distance

of an object over time .• Velocity Graphs •

V = distance time

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

• 1.The speed of sound in human tissue is

about 1600 m/s. If an ultrasound

pulse takes 1.5 x 10-5s to travel

through a tissue, what is the thickness

of the tissue?

A 2.4 km

B 2.4 m

C 23 cm

D 24 mm

Given:

speed= 1600m/s

Time = 1.5 x 10-5 s

Distance = speed x time

1600m/s x 1.5x 10 -5 s

=.024 m

= 24 mm

• 2. Joe Cool, Lee track star, ran 600 meters at 10m/sec. How long did it take Joe to run the race?

Distance= 600mSpeed = 10 m/sTime = distance/speed 600m / 10 m/s = 60s

The diagram represents the total travel of a teacher on a Saturday. Which part of the trip is made at the greatest average speed?

A QB RC SD T

Q= 14Km/12 min=1.17km/min

R= 12km/8min= 1.5 km/min

S = 15km/9 min =1.67 km/min- This is the greatest speed

Distance moved= 3cm time = 2second

Speed = 3cm/2 second =1.5 cm/s

Answer - A

AccelerationAcceleration (a) is the SLOPE of a VELOCITY (v) vs. time (t) graphPlotted on a distance vs. time graph, acceleration is an exponential curve The slope of a velocity –time graph represents ACCELERATIONAcceleration is a change in an objects velocity (speed or direction)

When an object’s speed changes over time it is accelerating (or decelerating)A = V final – V initial timeUnits for acceleration or m/s2

1. A fighter jet landing on aircraft carrier’s flight deck must reduce its speed from about 153 m/s to exactly 0 m/s in 2 s. What is the jet’s acceleration?

• A = Vfinal – Vinitial • time• 0 m/s – 153 m/s = -76.5 m/s2

• 2 s

• A = Vfinal – Vinitial • time• 6.5m/s-6.5m/s = 0 m/s2

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

Definition of a Force

• A Force is a push or a pull

The unit of force is Newton.

Balanced Force

• A force that produces no change in an object’s motion because it is balanced by an equal, opposite force.

Unbalanced Forces

Are forces that results in an object’s motion being changed.

Friction

A force that acts in a direction opposite to the motion of two surfaces in contact with each other.

Friction

Friction causes an object to slow down and stop.

Since the amount of energy stays constant, the energy becomes heat.

Answer –A . More force exerted less time it will take .

The table shows time required for the same toy car to travel 10 m across an identical section of a floor after it is pushed. The difference in times was probably caused by differences in ---

A force exerted

B surface friction

C air resistance

D car mass

Time (s)Trial

Toy Car Speed

A hockey player pushed a puck toward the opposite side of a level ice rink. The player expected the puck to continue all the way across the ice, but the puck slowed and stopped before reaching the other side. Which of these best explains why the puck failed to slide all the way to the opposite side?

A The puck’s temperature changed.

B An upward force acted on the puck.

C The puck’s momentum remained unchanged.

D An opposing force acted on the puck.

Answer:

D. An opposing force acted on the puck.

• Newton’s 1st Law-

Inertia or Newtons 1st Law

• Tendency for an object to stay at rest or moving in a straight line at a constant speed.

• The mass (symbol is “m”, measured in kg) of an object determines its inertia

Newton’s Second LawAcceleration is produced when a force acts on a mass. The

greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).

F = ma So, if the mass (m) is 1000 kg and the acceleration (a)

is .05 m/s2 then:

F = 1000 kg x .05 m/s2 = 50 N

• Weight (pull of gravity) is a commonly measured force (measured in N), calculated by F=mg, g is the acceleration due to gravity 9.8 m/s2

1. If the weight of an object is 60 N on earth what is its mass?

• Weight = mg

• Mass = weight / acceleration due to gravity

• 60 N / 9.8 m/s2

• 6.12 kg

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?

A 9.8 N

B 20 N

C 201 N

D 894 N

Force = m x a

a = 44.7 m/s- 0 m/s = 9.93 m/s2

m = 90.0 kg

F = 90.0 kg x 9.93 m/s2 = 894 N

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?

A What goes up must come down.

B For every action, there is an equal and

opposite reaction.

C The shape and size of an object affect air

resistance.

D The acceleration due to Earth’s gravity is

9.8 m/s2.

For every action there is an equal and opposite reaction.

The illustration above shows a student about to throw a ball while standing on a skateboard. Which illustration below correctly shows the skateboard’s direction of motion after the student releases the ball?

D. Since the ball will go forward ,so the student will go backward.

How much force is needed to accelerate

a 1,300 kg car at a rate of 1.5 m/s2?

A 867 N

B 1,950 N

C 8,493 N

D 16,562 N

Force = m x a

= 1300 kg X 1.5m/s2 =1950 N

A 16 NB 32 NC 88 ND 100 N

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?

Force = mass x acceleration

Mass of smaller skater = 40 kg

Acceleration of smaller skater = 3.0 m/s – 0 m/s = 2.5 m/s2

40 kg x 2.5 m/s2 = 100N

The picture above shows the direction in which water leaves the scallop’s shell. Which picture below shows the direction the scallop will move?

The scallop will move in the opposite direction.

15. What is the weight of a rock that has a mass of 5.0 kg?

• 0.51 N

• 49 N

• 0.51 Kn

• 49 kN

Weight = mg

= 5.0 kg x 9.8 m/s2 = 49 N

Answer: B

• 16. Airbags on cars are used to keep you from hitting the steering wheel of the car when the car hits a stationary object, because your body still has –

• resistance

• force

• potential

• inertia

D. INERTIA

Why use a machine?

• In an ideal (perfect) machine the work put into the machine equals the work put out by that machine (Win = Wout)

• Why is this impossible?

• No real machine is 100% efficient… They do not put out the same amount of work that is put in.

• Efficiency of a machine is work output / work input x 100 %

• Efficiency = Wout x 100%

Machines make work easier

• The ideal mechanical advantage (IMA) of a machine is the number of times the output force is larger than the input force IMA=Fout/Fin

• A machine can only make this happen by moving the input force through a farther distance than the output force

• Fin • din = Fout • dout

48 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?

G 12 J

H 18 J

J 21 J

Total work out put = 6N X 3m = 18 J

Work input = 30 J

Work converted to heat = 30 J -18J = 12 J

18a. An Automobile engine produces 15J of work for every 100J of energy consumed. What is the engine’s efficiency?

% Efficiency = work input x 100%

work out put

= 15 J x 100%

= 15 %

18b. If a machine is 36% efficient and can provide 75J of work output, how much work must be put in the machine?

Efficiency = Wout x 100% Win

36% = 75 J X 100% Win

Work input = 75 J X 100%

= 208 J

• Simple machines make our work easier by enabling us to use less mechanical effort to move an object. Often several simple machines are combined in complex machines.

• Remember, the ideal mechanical advantage of a

machine (IMA) is the number of times the output force is larger than the input force IMA = Fout/Fin

• A machine can only make this happen by moving the input force through a further distance than the output force

We use machines to reduce the amount of force applied, but at the sake of more TOTAL work required.

6 Types of simple machines

• Some Simple Machines:

• Inclined planes

• Screws

• Pulleys

• Wheel and axle

• Levers

• Wedge

Work• Work: using a force

for a distance

• W = F x d

• The work done by forces on an object = changes in energy for that object.

• Work and Energy are measured in Joules

• 1 Joule = 1 Newton • meter

When you push a wall and the wall does not move, the distance moved is zero, so the work done is zero too.

A accelerated rapidly

B remained motionless

C decreased its velocity

D gained momentum

45 If a force of 100 newtons was exerted on an object and no work was done, the object must have —

Work = Force x Distance

Work = 0 Force = 100 N so

0 J = 100 N x d

distance must be 0

It did not move!

42 How much work is performed when a 50 kg crate is pushed 15 m with a force of 20 N?

F 300 JG 750 JH 1,000 JJ 15,000 J

Use the formula Work = Force x distance

Force of 20 N x 15 meters = 300 Joules Answer:

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?

A 380 L

B 982 J

C 2,000 J

D 10,000 J

W= F X D

= 980N x 2.04 m = 2000J

A person pushes a large box across a level floor by applying a horizontal force of 200 N. If the person pushes the box a distance of 5 meters in 10 seconds, how much work does the person do on the box?

A 2000 joules

B 1000 joules

C 400 joules

D 100 joules

Work = F X D

200 N x 5 m = 1000 J

Answer: B

Energy

Is defined as the Ability to do Work

Energy has Two

Types: Kinetic (Energy of Motion) Kinetic (Energy of Motion) and and Potential (Stored Energy)Potential (Stored Energy)

Kinetic Energy

KE = ½ m v 2 Ex: A moving car has the ability to

do work on the light pole if it hits it.

A 1-kilogram ball has a kinetic energy of 50 joules. The velocity of the ball is ---

A 5 m/s

B 10 m/s

C 25 m/s

D 50 m/s

K.E. = ½ mv2

50 J= ½ (1 kg) v2

100= V2

V= 10 m/s

Circle the one that has more kinetic energy

• A 25 kg mass or a 30 kg mass going 5 m/s.

• Two 10 kg masses, one going 75 m/s, one going 45 m/s.

• A car at rest or a car rolling down a hill.

• A heavy bike or a light bike.

Potential Energy 2 possibilities

Potential energy (PE) is stored energy

1. Gravitational PEEx: Object lifted to some height

2. Elastic PE Ex: A stretched or compressed object (spring or rubber band )

Gravitational Potential Energy or “Will it fall?”

GPE = m g h

- m is the mass of the

object in kg,

- g is the acceleration

due to gravity which is

9.8 m/s2 on earth

- h is the height in meters

Law of Conservation of Energy

• Energy can change forms, but is never created nor destroyed

• Loss in one form = gain in an another form

• A falling object speeds up as it falls to the ground; PE decreases as KE increases. The KE it has at impact = the PE it had before it fell.

Example: A falling object speeds up as it falls to the ground;

PE decreases as KE increases, the KE it has at impact with the ground is equal to the PE it had before it fell

Energy can be conserved in Non-Mechanical forms

The chemical energy in a battery transforms into electrical energy

What is the approximate difference in gravitational potential energy of the two shaded boxes?

A. 19JB. 39JC. 59JD. 79J

GPE =m x g x h

2.0kg x 9.8m/s2 x 3.0 m =58.8 J

2.0kg x 9.8 m/s2 x 1 m =19.6 J

59.8-19.6= 39.2 J

What is the potential energy of the rock?

A. 59,000 joulesB. 64,600 joulesC. 93,100 joulesD. 121,600 joules

G.P.E = m x g x h = 95kg x 9.8m/s2 x 100m

= 93100 J

• Power: the rate at which WORK IS DONE.• P = Work/time• Power is measured in WATTS• 1 watt = 1 Joule 1 sec• Power can be increased by DECREASING

the amount of time needed to do the same amount of work.

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

Power = work / time

Work = force x distance

= 12054 N x 1.89 m = 22782 J

=22782J / 4.75s = 4796 W

A woman lifts a 57-newton weight a distance

of 40 centimeters each time she does a

particular exercise. It takes her 0.60 second

to lift the weight. How much power does she

supply for lifting the weight one time?

A 24 W

B 34 W

C 38 W

D 95 W

Make sure to convert distance to m!!

40 cm = .4 m

Work = f x d

= 57 N x .4 m

= 22.8 J

P= work / time

P= 22.8 J / .60s

= 38 W

An advertisement claims that a certain truck

has the most powerful engine in its class. If

the engine has more power, which of the

following can the truck’s engine do,

compared to every other engine in its class?

A Produce fewer emissions

B Operate more efficiently

C Perform work faster

D accelerate longer

C. Perform work faster.

Which of the following correctly states the law of conservation of energy?

A. Energy cannot be created or destroyed, but can be converted from one form to another.

B. Energy can be created or destroyed, as well as being converted from one form to another.

C. Energy is created when it is converted from one form to another.

D. In most some energy is destroyed

Answer - A

Momentum-

• Write the formula used to calculate momentum = m x v

• Unit of momentum = kg m/s

What is the law of conservation of momentum?

• In the absence of external forces, the total momentum of the system is conserved.

• So using this law we can write the following equation about the two colliding objects, having mass m1 and m2.

• (m1v1)i + (m2v2)i = (m1v1)f + (m2v2)f

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. That is, the momentum lost by object 1 is equal to the momentum gained by object 2.

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

Momentum = m x v

15 kg m/s = m x 30 m/s

15/30 = 0.5 kg

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?

A 300 kgm/s

B 200 kgm/s

C 150 kgm/s

D 0 kgm/s

Momentum of ball 1=

100 x 3= 300 kg m/s

Momentum of ball 2

150 x 2m/s= 300 kg m/s

The difference is 0 kg m/s

The 500 g cart is moving in a straight line at a constant speed of 2 m/s. Which of the following must to 250 g toy car have in order to maintain the same momentum as the cart?

A An acceleration of 5 m/s2 for 2 secondsB A potential energy of 20 JC A constant velocity of 4 m/sD An applied force of 5 N for 5 seconds

Momentum of cart

500 g x 2 m/s

1000 g m/s

Momentum of car

250 g x v = 1000 g m/s

v = 4 m/s

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?

Car velocity = 6.3 m/sDriver velocity = 6.3 m/sDriver mass = 100 kg

Car velocity = 0 m/sDriver velocity = 6.3 m/sDriver mass = 100 kg

Car velocity = 0 m/sDriver velocity = m/sDriver mass = 100 kg

6.3 m/s x 100 kg = 630 kg m/s

Velocity of all waves - v = f x λ

f - frequency is the number of vibrations in one second .The pitch of sound depends on it’s frequency.

λ - wavelength (distance between identical points on two consecutive waves)

Reflection - bounce off barriers in regular ways

Refraction - waves can change direction when speed changes. Light waves bend when they move from air into water.

Resonance - the tendency of a system to vibrate at maximum amplitude at certain frequencies

Draw and label the parts of a transverse wave

Define frequency

Number of vibrations in one second

Which illustration best demonstrates compression waves?

A tuning fork with a frequency of 256 Hz vibrates when struck. Because of these vibrations, a nearby tuning fork begins to vibrate without being struck. Which of the following best accounts for the vibrations of the second tuning fork?

A. ResonanceB. PolarizationC. DiffractionD. Refraction

A. Resonance

Which label on the model represents a wavelength?

When a DVD is read, laser light touches the DVD surface and is then measured at location A. What allows light to return to location A after striking the DVD surface?

A. ConductionB. RefractionC. MagnificationD. Reflection

Laser Light Striking a DVD

D. reflection

The pitch of a sound made by plucking a guitar string is determined by the ---

A. frequency of the vibration producedB. strength of the plucking forceC. distance between the stringsD. 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?

Which wave has the least velocity?

Use formula chart v = f x λ

V = 1 m x 2 Hz = 2 m/s V = 2 m x 8 Hz = 16 m/s

V = 3 m x 3 Hz = 9 m/s V = 4 m x 1 Hz = 4 m/s

A. ReflectionB. RefractionC. DiffractionD. Polarization

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 the air. The bending of light as it passes from one medium into another is known as ---

Bending of light is called refraction.

Electrical Energy - Moving electrons in a path is

electricity• Electrical Potential Difference (ΔV) is measured

in Volts (V)• The rate of moving electric charges is called

current (I) and is measured in Amperes (A)• Opposition to the movement of the current is

called Resistance (R) and is measured in ohms (Ω).

Circuits – 2 types

• Series circuits are the most simple.

• One (1) path for the current to travel.

• Contains an energy source, a path, and a load (something for it to do, like a lamp)

Circuits – 2 types• Parallel circuits

provide more than one path for the current to travel.

• Most circuits are parallel, since if one lamp goes out, the others can stay lit.

In this circuit, how much current flows through the lightbulb?

A. 0.75 ampB. 1.50 ampsC. 2.0 ampsD. 3.0 amps

V= 1.5 V

R= 2.0 ohm

V = I x R

I = V / R

I = 1.5 V / 2.0 ohms

I = 0.75 amp

F. QG. RH. SJ. T

Which switches, if opened, will cause the light bulb to stop glowing?

It is the only switch in series to both the battery and light.

USE THE FORMULA SHEET!!

• What is the current in a copper wire that has a resistance of 2 ohms and is connected to a 9 volt electrical source?

A. 0.22 amp

B. 4.5 amps

C. 11.0 amps

D. 18.0 amps

V = I R so,

9V = I x 2 ohms or 4.5 amps

Which circuit is built so that if one lightbulb goes out, the other three lightbulbs will continue to glow?

Parallel circuit

Conduction – Transfer of heat by direct contact. Conduction takes place in solids .

Convection- Heating by circulating fluids . Takes place in liquids and gases. Air currents are caused by convection.

Radiation - When infrared radiation heats up objects.

Sun’s heat reaches us by radiation.

In which container is the substance unable to transfer heat by convection?

Solids are unable to transfer heat by fluid motion which is called convection .

The temperature of water increases by 8oC when the metal block is added. Which could cause the temperature of the water to increase by 10oC after the metal block is added?

A.Using 500 g of waterB.Using a larger beakerC.Adding more 20oC waterD.Adding heat to the metal block

D. Adding heat to the metal block.

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 ---

A. ConductionB. ConvectionC. RadiationD. Compression

A. Conduction

In winter the air just above the top bunk of a bunk bed is warmer than the air just above the bottom bunk because warm air rises. Which of the following describes the method of heating that causes this difference in temperature?

A. Radiation from the roomB. Heat transfer through wallsC.Convection currents in the roomD.Heat conduction through the bed

Air currents are caused by convection .

Renewable sources of energy - Sun , Water, Wind.

These cause no pollution .

The drawback of solar energy is it cannot be used on a cloudy day.

Fossil fuels like coal and petroleum are non renewable and cause a lot of pollution.

The gases (i.e. sulfur dioxide) given off by fossil fuels cause acid rain.

A company has decided to market itself as environmentally friendly. If the company is going to sell calculators, the use of which energy source would produce the fewest by-products and the least waste?

A. Rechargeable batteries

B. Solar cells

C. Dry-cell batteries

D. Tesla coils

B. Solar cells

Which of these is an advantage of producing electricity using solar power plants rather than using coal-fired plants?

A. Solar power plants can operate for about 10 hours a day.

B. Solar power plants can produce variable amounts of energy.

C. Solar power plants produce fewer pollutants.

D. Solar power plants require continuous sunlight.

C. Solar power plants produce less pollutants.

C. Can be used many times.

One economic benefit of using rechargeable batteries instead of disposable batteries is that rechargeable batteries ---

A. are cheaper to manufactureB. can be packaged in small containersC. can be used many timesD. generate their own electricity

Which of these devices uses the sun’s energy directly?

A. WindmillB. Hydroelectric damC. Nuclear power plantD. Photovoltaic cell

D. Photovoltaic cell

Which of these produces most of the compounds responsible for causing acid rain?

A. Nuclear fissionB. Fossil fuelsC. Solar cellsD. Windmills

Fossil Fuels

This picture shows a small section of a solar power plant. Which of these decreases the energy production at such power plants?

A. Cloudy skiesB. Ozone in the airC. Hot weatherD. Low humidity

Cloudy Skies

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