Review TAKS 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. 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 = D

2. Joe Cool, Lee track star, ran 600 meters at 10m/sec 2. Joe Cool, Lee track star, ran 600 meters at 10m/sec. How long did it take Joe to run the race? Distance= 600m Speed = 10 m/s Time = distance/speed 600m / 10 m/s = 60s

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

When an object’s speed changes over time it is accelerating (or decelerating) A = V final – V initial time Units for acceleration or m/s2 Acceleration Acceleration (a) is the SLOPE of a VELOCITY (v) vs. time (t) graph Plotted on a distance vs. time graph, acceleration is an exponential curve The slope of a velocity –time graph represents ACCELERATION Acceleration is a change in an objects velocity (speed or direction)

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 4 s

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. If you were to add these forces they would = 0

Unbalanced Forces Are forces that results in an object’s motion being changed. + = Add together to equal greater force.

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. Air resistance is an another example of friction. Lubricants or grease reduce friction.

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

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 Inertia comes from the Latin word meaning lazy.

Newton’s Second Law Acceleration 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

Force = m x a a = 44.7 m/s- 0 m/s = 9.93 m/s2 4.5 s m = 90.0 kg F = 90.0 kg x 9.93 m/s2 = 894 N

For every action there is an equal and opposite reaction. B. For every action there is an equal and opposite reaction. s2

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

Force = m x a = 1300 kg X 1.5m/s2 =1950 N

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 1.2 s 40 kg x 2.5 m/s2 = 100N

D. 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 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% Win

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

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% 100 J = 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% Work input = 75 J X 100% 36% = 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.

W= F X D = 980N x 2.04 m = 2000J

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) and 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.

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 PE Ex: 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

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

G.P.E = m x g x h = 95kg x 9.8m/s2 x 100m = 93100 J

Power 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.

Power = work / time Work = force x distance = 12054 N x 1.89 m = 22782 J =22782J / 4.75s = 4796 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

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.

Momentum = m x v 15 kg m/s = m x 30 m/s 15/30 = 0.5 kg

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

2 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 2

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

B.

A. Resonance

A.

D. reflection

A.

B.

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 Use formula chart v = f x λ

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.

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

Which switches, if opened, will cause the light bulb to stop glowing? Q R H. S J. T It is the only switch in series to both the battery and light.

USE THE FORMULA SHEET!! V = I R so, 9V = I x 2 ohms or 4.5 amps 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

D. Parallel circuit

Conduction – Transfer of heat by direct contact 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.

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

D. Adding heat to the metal block.

A. Conduction

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.

B. Solar cells

C. Solar power plants produce less pollutants.

C. Can be used many times.

D. Photovoltaic cell

B. Fossil Fuels

A. Cloudy Skies