Physics Concept Review

Transcription

1 Physics oncept eiew Newton eelope 3 laws that goern motion of eerything Newton s Law Definition Example FIST LW (the law of inertia) an object at rest will remain at rest an an object in motion will remain in motion unless acte upon by a net force SEOND LW summe up by equation or can also write as a = F = ma F m THID LW for eery action there is an equal an opposing reaction Strength of Forces Forces hae similarities an ifferences FOE TTTIVE EPULSIVE STENGTH Fα Fα Graitational Yes No Fα Electrical Yes Yes Magnetic Yes Yes With all three of the forces, it is the istance between the two objects (masses, charges, magnets) that hae the greatest effect on the strength of the force. ll three obey the inerse square law Fα (Force is proportional to one oer the istance square)

2 EQUTION EXMPLE POLEM SOLUTION = = t = t t = 0 at gt = 0 0 = initial elocity = final elocity MOTION ND FOES EQUTIONS. You rop a rock off the top of a 50 meter tall builing an it takes 5 secons to hit the groun. What is the rocks aerage spee?. You trael in a car going 45 miles/hour for hours. How far hae you traele 3. How long woul it take to trael 00 meters at 5m/s?. You rop a rock off the top of a 0 meter tall builing an it hits the groun.5 secons later. How fast was it traeling when it hit the groun? 50 = = 0m / s t 5 = t = ( 45 )( ) = miles = t = = = 8 s 5 = 0 gt ( 9.8)(.5) 4.7 m s = 0 = / a = F m F = ma m = F a F graity = mg Force graity = weight g = 9.8 m/s W = F. 8 Newton force is applie to 4 kilogram block on a frictionless table. What is the acceleration of the block?. You are staning on a skateboar an your frien pushes you with a force of 90 N. If your mass is 60 kg, what will your acceleration be? 3. 6 kilogram block is accelerate at m/s by a force on a frictionless surface. What was the force require to o this? 4. What is the mass of an object that is accelerate at m/s with a Force of 5 N?. What is the force of graity on an object with a mass of 0 kg on the Earth?. How much work is one when you apply a 6 Newton force an moe an object 0 meters on a frictionless surface? F 8 a = = = m 4 m / s F 90 a = = =.5m / s m 60 ( 6 )( ) = N F = ma = F 5 m = = = 5kg a ( 0 )( 9.8) = N F graity = mg = 98 ( 6 )( 0) = J W = F = 60 alculate Net Force

3 ONSEVTION OF ENEGY ND MOMENTUM EQUTIONS EQUTION EXMPLE POLEM SOLUTION KINETI ENEGY E = m GVITTIONL POTENTIL ENEGY E = mgh. 5.0 kg mass is moing with a spee of.0 m/s. What is the kinetic energy of the mass?. 0 kg object is roppe from a height of 0 meters aboe the groun. What is its kinetic energy the moment before it hits?. hyraulic lift use at an automotie repair shop raises a 500-kilogram car meters off of the groun. What is the potential energy gien to the car? Know that all of its potential energy is conerte into kinetic energy as it falls = E = ( 5)( ) = J E = 0 ( 0 )( 9.8)( 0) = J E = mgh = 9800 mgh ( 500 )( 9.8)( ) = 4900J MOMENTUM p = m p m = p = m p before = p after. What is the momentum of a 5 kg object moing at 0 m/s?. What is the mass of an object with a momentum of 5 kg m/s an a elocity of 5 m/s? 3. What is the elocity of an object that has a momentum of 40 kg m/s an a mass of 0 kg?. 000 kg boxcar traeling 0 m/s collies an couples with another boxcar at rest. If there final couple elocity is 5 m/ s, what is the mass of the secon boxcar? mass = 000kg mass =? ( 5)( 0) = 50kg m s p = m = / p 5 m = = = 5kg 5 p 40 = = = m s m 0 / p before = p after alculate total momentum before: p before ( 0 x000) (? 0) = 0, 000 = x Since Momentum before = momentum after, the final momentum = 00 kg m/s ( m)( 5m s) 0,000kg m/ s = / 0,000 m = = 000kg 5 Since the first boxcar ha a mass of 000kg, the secon boxcar must hae a mass of: 000kg -000kg = 000kg

4 WVE EQUTIONS EQUTION EXMPLE POLEM SOLUTION λf. stuent shakes the en of a rope with a frequency of.0 Hz, causing waes with a waelength of 0.5 m to trael along the rope. What is the elocity of the waes? = = ( 0.5)( ) = m / s λ = f = f λ. tuning fork is use to prouce soun waes with a frequency of 688 hertz. The waes trael through the air at 344 m/s. What is the waelength of the soun waes? 3. What is the frequency of a soun wae traeling at 344 m/s that has a waelength of 0. meters? λ = f = 344 = 0.5m f = = = 3, 440hertz λ 0. Wae type TNSVESE WVE Description Examples: electromagnetic waes, shaking a rope up an own, ocean waes Wae motion is perpenicular to the irection the wae traels LONGITUDINL WVE Examples: soun waes, slinky Wae motion is in the same irection the wae is traeling.

5 ONEPTS ENTOPY measure of isorer. Disorer increases; entropy increases Natural orer of things is to become more isorere (greater entropy) Secon Law of Thermoynamics states that for natural processes, in the long run, entropy always increases. HET HET- the energy that transfers from one object to another because of temperature ifference between them Temperature-proportional to the aerage kinetic energy of molecules Heat always traels from hot object to coler object Thermal equilibrium- after objects in thermal contact with each other reach the same temperature, no heat flows between them IMETLLI STIP Different materials expan at ifferent rates. imetallic strip-two strips of ifferent metals. When heate, the ifference in the amounts of expansion cause strip to ben Thermostat- practical application of bimetallic strip Thermal equilibrium- after objects in thermal contact with each other reach the same temperature, no heat flows between them Thermostat- The back an forth bening of bimetallic coil opens an closes an electric switch that turns on the heat

6 ONEPTS DOPPLE EFFET The apparent change in frequency (pitch) ue to the motion of the source (or receier). Higher frequency (pitch) when source moing towars you Lower frequency (pitch) when soun source moing away from you. Doppler effect use by astronomers to etermine rotation of stars, galaxies (re shift /blue shift ELETOMGNETI SPETUM Shows range of electromagnetic waes Electromagnetic wae- wae that is partly electric an partly magnetic (transerse wae) Light is an electromagnetic waes (below re - infrare, aboe iolet - ultraiolet) Visible light - OYGIV WVE INTEFEENE Waes can interact with each other an the wae effects can be increase, ecrease, or neutralize. onstructie interference- waes a together (increase amplitue) Destructie interference- when trough of one waes oerlaps the crest of another wae (ecreases amplitue or can cancel) WVE SPEED Spee of wae epens on the meium it traels through Soun waes o not trael in a acuum Spee of soun = 344 m/s (room temperature at sea leel) Spee of light = 300,000 km/s (in a acuum)

7 ONEPTS LW OF ONSEVTION OF ENEGY Energy is not create or estroye, it is only transforme from form to another. (Example below: Graitational Potential Energy into Kinetic Energy) Notice that the total energy is always the same. Total energy equals KE PE. You will use this fact to sole certain problems asking to sole for kinetic energy when you are not gien the elocity. In this case, sole for its initial PE an then know that it is conerte into KE as it falls. LW OF ONSEVTION OF MOMENTUM In the absence of an external force, the momentum of a system remains unchange ELSTI OLLISION When objects collie without being permanently eforme an without generating heat INELSTI OLLISION Wheneer colliing objects become tangle or couple together. HINT: To sole problems inoling collisions, remember that the total momentum before will equal the total momentum after.

8 ONEPTS UNIFOM IUL MOTION entripetal force- center seeking points to center of circle (force that is at right angle to the path of moing object an tens to prouce circular motion entrifugal force- center fleeing Not a real force but attribute to inertia (tenency of moing boy to follow a straight line path) UNIVESL GVITTION Law of Uniersal Graitation propose by Isaac Newton pplies to eery object in unierse Inerse square law- Force is proportional to inerse square of istance Fα MGNETISM Magnetism cause by both orbital motion an spinning motion of eery electron in an atom Magnets are polarize (hae North pole an South pole) Magnetic fiel- exit north pole an enter south pole. Fiel lines always forme close loops moing charge prouces a magnetic fiel (electric current) FIST IGHT HND ULE (Direction of magnetic fiel an current) SEOND IGHT HND ULE (Determining polarity of electromagnet) ELETIITY Forces attractie an repulsie (like charges repel, an unlike attract) Static Electricity- stationary charge urrent Electricity-moing charge onuctor- electrons moe freely (metals) Insulator-electrons o not moe freely (rubber, glass)

9 ELETIITY EQUTIONS EQUTION EXMPLE POLEM SOLUTION Ohm s Law I = V Power (P) P=IV Series ircuit I = V source V = V V.... What is the current in a circuit with a V battery an a resistance of 6 ohms?. What is the Power in the circuit aboe?. What is the current in the circuit below if each resistor has a resistance of ohms? V I = = = 6 P= IV P = ( )( ) = 4Watts First you will nee to calculate the totat resistance in this series circuit. = = 6Ω Then plug in V an an sole for I. V 6 I = = = 6 = source Parallel ircuit I = V... V = V = V = V I = I I I. What is the oltage rop at each resistor aboe?. What is the current in each of the branches of the parallel circuit below if each of the resistors is 3 ohms?. What is the total current in the parallel circuit aboe? To sole you simply iie the oltage source by the number of resistors. 6/3 = olts each emember that the oltage in each branch is equal to the source oltage V = V = V = V source I = = 6 I = = 6 I = = 3 4 I = I I I I = = 5 = 3. What is the equialent resistance in the parallel circuit aboe 5 = = = 6 =. Ω