Momentum Quiz Review KEY - We Love Science - Home



4752975000-85725-6667500lefttop00righttop00righttop00Momentum Quiz Review KEYInstructions: Show your work completely in your journal when answering the following questions. If a 3.0 kg object moves 10. meters in 2.0 seconds, what is its average momentum?v=dt=10 m2.0 s=5.0 msp=mv=(3.0 kg)(5.0 ms)p=15 N?sAn impulse of 30.0 N?s is applied to a 5.00 kg mass. If the mass had a speed of 100. ms before the impulse, what would its speed be after the impulse?I=m??v=mv2-v2?v2=Im+v2=30.0 N?s5.00 kg+100msv2=106 msA 15 N force acts on an object in a direction due east for 3.0 seconds. What will be the change in momentum of the object?I=F??t=(15 N)(3.0 s)I=?p=45 N?sA 1.0 kg mass changes speed from 2.0 ms to 5.0 ms. What is the change in the object’s momentum??p=m??v=mv2-v1=1.0 kg(5.0ms-2.0ms)?p=3.0 N?sA net force of 12 Newtons acting North on an object for 4.0 seconds will produce an impulse of what?I=F??t=(12 N)(4.0 s)I=48 N?sA ping-pong gun originally at rest fires a ball. What is the sum of the gun’s and ball’s momenta after the shot?pbefore=p'after=0 N?sA moving freight car runs into an identical car at rest on the track. The cars couple together. Compared to the velocity of the first car before the collision, what is the velocity of the combined cars after the collision?pbefore=p'afterm1v1+m2v2=m1+m2 v '?mv1+0=2mv '? v '=12v1If a 54 N?s impulse is given to a 6.0 kg object, what is the object’s change in momentum?I=?p=54 N?sWhich quantities do not always occur in equal and opposite pairs when and interaction takes place within a system?Impulses TRUEAccelerationsFALSEForcesTRUEMomenta changesTRUEObject A has a momentum of 60.0 N?s. Object B, which has the same mass, is standing motionless. Object A strikes object B and stops. If the mass of object B is 6.0 kg, what is the velocity of object B after the collision?pbefore=p'afterm1v1+m2v2=m1v'1+m2v'2?60 N?s+0=0+(6.0 kg)v'2v'2=10. msMomentum and Energy Quiz Review KEYInstructions: Show your work completely in your journal when answering the following questions.Define the following (conceptual definition and equation):MomentumMomentum is similar to inertia in motion; p=m?vImpulseImpulse is a force applied over a time interval; I=F?t=?pConservation of MomentumThe momentum of a system before an event is equal to momentum afterward. pbefore=p'afterKinetic EnergyEnergy due to motion; EK=12mv2Potential EnergyEnergy due to position/location; EP=mghMechanical EnergyEnergy due to motion or location of a physical body; ME=EK+EPConservation of EnergyMechanical energy of a system remains constant before and after an event; EK1+EP1=E'K2+E'P2Elastic CollisionA collision where objects bounce off each other undamaged; m1v1+m2v2=m1v'1+m2v'2Inelastic CollisionA collision where objects bounce off and each is damaged OR objects collide and stick together;m1v1+m2v2=m1+m2 v 'What is the kinetic energy for the following objects?A 65 kg runner moving with a speed of 7.0 msEK=12mv2=1265 kg(7.0 ms)2EK=1600 JA 2.0 million kg space shuttle with a launch speed of 44 msEK=12mv2=122000000 kg(44 ms)2EK=1.9×109 JA 5.0 kg bowling ball moving with a speed of 9.5 msEK=12mv2=125.0 kg(9.5 ms)2EK=230 JA 75 kg skier at restEK=12mv2=1275 kg(0 ms)2EK=0 JWhat is the potential energy for the following objects?A 0.50 kg orange sitting on a shelf 2.0 meters off the groundEP=mgh=0.50 kg9.80 ms2(2.0 m)EP=9.8 JA 68 kg snowboarder sitting on a ramp 15 meters highEP=mgh=68 kg9.80 ms2(15 m)EP=1.0×104 JA 1200 kg car parked in a garage 6 stories up (21 meters)EP=mgh=1200 kg9.80 ms2(21 m)EP=2.5×105 JA 16 kg box sitting on the floorEP=mgh=16 kg9.80 ms2(0 m)EP=0 JYou decide to apply your vast knowledge of physics to baseball. You swing the bat and, oops, it’s a pop up. The 0.145 kg ball starts straight up off the bat at 35 ms. How much kinetic energy does the ball have initially? At the top? EK(1)=12mv2=120.145 kg(35 ms)2EK(1)=89 JE'K(2)=0 JAt the top, what is the ball’s potential energy?EK1+EP1=E'K2+E'P2?89 J+0=0+E'P2E'P2=89 JThe catcher catches the ball. Just before it hits, what is the ball’s kinetic energy? Potential energy?Kinetic energy is conserved in an elastic collision. Thus:EK=89 JEP=0 JYou go next door from the baseball field and find the local pool. You climb up onto the 10. m platform to take a dive. If your mass is 50. kg:What is the change in potential energy when you climb up there??EP=EP(2)-EP1=mgh2-mgh1=50 kg9.80 ms210 m-0?EP=4900 JYou jump. How fast are you going just before striking the water 10. m below?EK1+EP1=E'K2+E'P2?0+4900 J=E'K2+0E'K2=4900 JE'K(2)=12mv2?4900 J=1250 kgv2v=14 msA world-class Olympic athlete starts from rest on top of a 100. meter hill, skis down the incline and makes a world-record setting jump. If she has a mass of 55 kg, use the information given in the diagram to fill in the missing information.center43815 KE = 22,000 Jh = __________ mPoint APoint DPoint CPoint DPoint E00 KE = 22,000 Jh = __________ mPoint APoint DPoint CPoint DPoint E Point A: EP=mgh=55 kg9.80 ms2100 m=53,900 JEK=12mv2=0 JME=EK+EP=53,900 JPoint C: ME=constant=53,900 JEP=mgh=55 kg9.80 ms230 m=16,170 JME=EK+EP?EK=ME-EP=53900 J-16170 J=37,730 JPoint D: ME=constant=53,900 JEK=22,000 JME=EK+EP?EP=ME-EK=53900 J-22000 J=31,900 JEP=mgh?h=EPmg=31900 J55 kg9.80 ms2=59 mPoint E: ME=constant=53,900 JEP=0 JME=EK+EP?EK=53,900 JCalculate her velocity at points B and C Point B (equivalent to point D since they’re at the same height!): EK=12mv2=22,000 JvB=2EK(B)m=2(22000 J)(55 kg)vB=28ms Point C: EK=12mv2=37,730 JvC=2EK(C)m=2(37730 J)(55 kg)vB=37ms 239395134683500Use the law of conservation of energy to fill in the blanks at the various marked positions for a 1000. kg roller coaster car.center157480EP=mgh?h=EPmg=450000 J1000 kg9.80 ms2 ?h=46 mEK=0?vB=0msME=EK+EP?EK=ME-EP=450000 J-200000 J?EK=250,000 JEP=mgh?h=EPmg=200000 J1000 kg9.80 ms2 ?h=20. mEK=12mv2=200,000 ?vB=2EK(B)m=2(250000 J)(1000 kg)?vB=22msME=EK+EP?EK=450,000 JEP=mgh?EP=0 JEK=12mv2=400,000 ?vB=2EK(B)m=2(450000 J)(1000 kg)?vB=30.msUnit 5 Test Review KEYInstructions: Show all of your work completely in your journal, including the equations used in variable form. Pay attention to sig figs and units; use complete sentences if applicable. In your own words, define the following terms. Include the conceptual definition, equation(s) and unit(s):MomentumMomentum is similar to inertia in motion; p=m?v; the units are kgms or N?s.ImpulseImpulse is a force applied over a time interval; I=F?t=?p; the units are kgms or N?s .Conservation of MomentumThe momentum of a system before an event is equal to momentum afterward. The units are kgms or N?s.pbefore=p'afterKinetic EnergyEnergy due to motion; EK=12mv2; the units are Joules ( J ).Potential EnergyEnergy due to position/location; EP=mgh; the units are Joules ( J ).Mechanical EnergyEnergy due to motion or location of a physical body; ME=EK+EP; the units are Joules ( J ).Conservation of EnergyMechanical energy of a system remains constant before and after an event; the units are Joules ( J ).EK1+EP1=E'K2+E'P2WorkWork is defined as the transfer of energy through motion. Its equation is W=F?d?cosθ and the units are N?m or Joules ( J ). Work-Energy TheoremWork is directly related to a change in kinetic energy. This is called the work-kinetic energy theorem. The equation for this is W=?EK=EK2-EK1 and the units are N?m or Joules ( J ).PowerPower is defined as the rate at which work is done. Its equation is P=Wt and the units are Js or Watts (W). Compare and contrast elastic and inelastic collisions. Make sure that you discuss what quantities are conserved in these types of collisions!An elastic collision is one in which objects bounce off each other undamaged; momentum and kinetic energy are conserved. An inelastic collision is one in which objects bounce off and each is damaged OR objects collide and stick together; momentum is conserved, but kinetic energy is NOT conserved. What are the relationships between the following quantities (i.e. – inverse, directly proportional, etc.)? Momentum and VelocityDirectly: p α vImpulse and TimeDirectly: I α ?tForce and TimeInversely: F α 1?t Impulse and Δ MomentumDirectly: I α ?pKinetic and Potential EnergyInversely: EK α 1EP Kinetic Energy and VelocitySquared: EK α v2 Potential Energy and HeightDirectly: EP α hWork and ForceDirectly: W α FWork and Δ Kinetic Energy Directly: W α ?EKPower and WorkDirectly: W α PPower and TimeInversely: P α 1t If you fire a bullet from a pistol and a revolver with a longer barrel, which will have greater velocity when it leaves the barrel? Why? Because the force stays the same and the time it is applied over increases, the impulse increases. Since impulse is directly proportional to change in velocity, this means it will have a greater velocity. You are having a water balloon fight with your friends. Why are your water balloons more likely to break if you hit a friend who is not prepared versus letting them catch it?A friend who catches the balloon will most likely move their hand with the motion of the balloon, thus increasing the time over which the balloon comes to rest. This means that the force experienced by the balloon has a smaller magnitude and is less likely to break.Which is more damaging: running into a solid wall or colliding head on (with the same speed from the wall) with an identical car moving at the same speed? Why?They are both equally damaging! Think about the Myth Busters clip: Newton’s 3rd law means that they are both experiencing the same force!Two skiers are moving toward each other and collide. If the come to rest at the point of impact, what do we know about their motion before the collision?They had equal and opposite momentums before the collision. We know this because the total momentum after their collision is 0, so it must have been 0 before! (Since we don’t know their masses, we cannot say their velocities were equal and opposite. We need more information for that). When we talk about work, we are looking at a force causing motion. What forces are doing work in the following situations? These forces must be causing the motion and in the same direction as the displacement!A box is pushed 5 meters across the floor The applied push forceA sky-diver falls 100 meters towards the EarthThe force due to gravityAn elevator is lifted 20 meters upwardThe of tension in the cableWhy is it important for work to depend on displacement versus distance? What do we know about work as a result?Displacement is a vector! As a result, work is independent of the path taken! All that matters is the starting and ending points!Two boats of unequal mass travel across the bay at the same speed and in the same direction. If the water exerts the same frictional force on the boats, how will their stopping distances compare?They will have the same stopping distance. This is because the distance only depends on the force and the work. Since both are equal, they stop in the same distance; mass is not a factor!Basketball A and B each have a mass of 3.0 kg and are moving at 4.0 ms.What is Basketball A’s momentum? Basketball B?pA=pB=mv=(3.0 kg)(4.0 ms)pA=pB=12 kgmsIf A and B are moving in the same direction, what is the momentum of the system? What if they move in opposite directions?ptotal=pA+pB=12 kgms+12 kgms=24 kgmsptotal=pA+-pB=12 kgms-12 kgms=0 kgmsA roller coaster cart starts at the bottom of a hill with some speed. At some point while moving up the hill, the cart has a potential energy of 80.0 J and a kinetic energy of 20.0 J. When the cart is at the top of a hill and at rest, what is its potential energy?ME=constant=EK+EP=80.0 J+20.0 J=100. JAt the top of the hill, velocity is 0 so kinetic energy is 0 J:EP=100. JWhat was the initial speed of the cart at the bottom of the hill if it has a mass of 85.0 kg?At the bottom of the hill, height is 0 m so potential energy is 0 J:EP=100. J=12mv2v=2EKm=2(100 J)(85 kg)v=1.53 msAn ice skater is at rest on the ice when she catches a prop that her partner threw to her. If the skater has a mass of 55 kg, the prop is 7.0 kg, and it was initially moving towards her at 18 ms, how fast will the skater with the prop be moving after she catches the prop?pbefore=pafter?m1v1+m2v2=m1+m2 v '0+7.0 kg18 ms=55 kg+7.0 kgv '126 kgms=62 kgv 'v'=2.0 msWhat is the work done by a 35 N force exerted at an angle of 25° to push a box of tools 15 m?W=F?d?cosθ=35 N15 mcos25°W=480 N?mWhat is the power supplied by a constant 75 N force if the object has an average speed of 12 ms?P=Wt=F?dt=F?v=(75 N)(12 ms) P=900 WUnit 6 Quiz Review: Waves, Wave Behavior, and Sound ANSWER KEYInstructions: Show all of your work completely in your journal, including the equations used in variable form. Pay attention to sig figs and units; use complete sentences if applicable. Define and provided examples for the following types of waves:Transverse: waves with particle motion perpendicular to wave propagation (i.e. – guitar strings, earthquake S-waves)Longitudinal: waves with particle motion parallel to wave propagation (i.e. – sound waves, earthquake P-waves)Surface: waves with particle motion perpendicular AND parallel to wave propagation, resulting in a circular motion (i.e. – water waves)What is the only factor that affects the speed of a mechanical wave?Wave speed is a property of the medium through which the wave is travelling. Define and list the variables for the following terms:Frequency: The number of complete cycles that pass a fixed point every second; units: Hertz (Hz)Period: The amount of time required to complete on full cycle; units: seconds (s)Wave Speed: The speed with which energy propagates through a medium; units: m/s Amplitude: For transverse waves: amplitude is a measure of maximum displacement from equilibrium. In longitudinal waves: it is the difference in pressure between the compressions and rarefactions (perceived as volume in sound waves).Wavelength: The distance from one point on a wave to the same point on the next wave (i.e.- crest to crest); units: meters (m)Sound Intensity: power of sound per unit areas; units: decibels (dB)Sketch and label the following diagrams:Transverse Wave:40709855080CrestCrest36423607620170878564770003896360151765TroughTrough333756012573000Longitudinal Wave:Define and sketch a diagram for each of the following wave behaviors:29203651524000Constructive InterferenceDestructive Interference169926014033500Reflection171831017018000Refraction1861185571500DiffractionWhat is the superposition principle? What does it mean for mechanical waves? The superposition principle states that waves can be in the same place at the same time. To find the resultant wave’s amplitude, we simply add the two waves point by point. Define pitch; what wave property is it most closely related to?Pitch is the tone of a sound (how high or low something sounds). It is most closely associated with frequency. Define loudness; what wave property is it most closely related to?Loudness is the brain’s interpretation of pressure differences in sound waves. This is related to the amplitude of the sound wave. If frequency changes, what other wave properties are changed? Are they directly or indirectly related? If frequency changes (and the medium is not), the period changes inversely (i.e. – if frequency increases, period decreases), as does the wavelength (also inversely). How does air temperature affect the speed of sound? List an equation to support your reasoning.Yes! Sound travels faster in warmer air because the molecules have more kinetic energy and are thus easier to propagate through.vsound=331+0.6TExplain how the following parts of your ear are related to your ability to hear:Eardrum: The eardrum vibrates when sound waves reach it; these vibrations are then carried as pressure waves to the middle ear.Hammer: The hammer is a small bone in the middle ear; it vibrates due to pressure waves from the eardrum. Anvil: The anvil is a small bone in the middle ear; it vibrates due to vibrations from the hammer bone.Stirrup: The stirrup is a small bone in the middle ear; it vibrates due to vibrations from the anvil bone. It then transmits pressure waves to the inner ear.Cochlea: The cochlea has tiny hairs connected to nerve receptors. These hairs vibrate due to the pressure wave created by the bones in the middle ear. These hairs create electrical impulses that are sent to the brain and interpreted as sound! Define the following terms:Infrasonic frequencies: frequencies LOWER than 20 HzUltrasonic frequencies: frequencies HIGHER than 20,000 HzSubsonic speeds: speeds SLOWER than the speed of sound (~343 m/s)Supersonic speeds: speeds FASTER than the speed of soundDefine the Doppler Effect. How does the apparent frequency shift for an observer based on the motion of the source?The Doppler Shift is the APPARENT shift in frequency due to the relative motion of a sound source to an observer. When the source is moving TOWARDS the observer, the pitch the observer hears will be HIGHER than the source frequency and vice versa! A tuning fork with a frequency of 480 Hz is played in a room with a temperature of 25°C.What is the period of the sound wave? f=1T?T=1f=1480 HzT=0.00208 s=2.08×10-3sWhat is the velocity of the sound wave produced? vsound=331+0.6T=331+0.625℃vsound=346msWhat is the wavelength of the resulting sound wave?v=fλ?λ=vf=346ms480 Hzλ=0.721 m=721 mm17780-228600Physics Semester 2 Final: Equation SheetCLASS COPY00Physics Semester 2 Final: Equation SheetCLASS COPYPhysical Constantsg = 9.80 ms2vsound=343msIo=1×10-12Wm2vlight=3.00×108msUnit 1 Conversion Factors:1 mi = 1609 m1 in = 2.54 cm1 hr = 3600 s1 kg = 2.2 lbs1 lb = 454 g1 cm3 = 1 mLUnit 2 (Kinematics) Equations:Linear Motion:v=d t so t=dv and d=v?tv=v1+v22Δv=v2-v1a=v2-v1tv2=v1+atv22=v12+2add=v1t+12at2Free Fall Motion:v=g?td=12gt2Unit 3 (Vectors and Projectiles) Equations:Vector Addition:sinθ=oppositehypotenusecosθ=adjacenthypotenusetanθ=oppositeadjacenta2+b2=c2R=Rx2+Ry2θ=tan-1RyRxProjectile Motion:vvert initial=vinitial?sinθΔvvertical=g?tvvert (final)=g?tdowntup=vvert (initial)gdvertical=12gt2vhorizontal=vinitial?cosθdhorizonal=vhorizonal?ttotaldhorizonal=range=vinitial2?sin2θgttotal=tup+tdownUnit 4 (Forces and Newton’s Laws) Equations:Fnet=m?aFg=m?gVertical Motion:Fup=m(a+g)Fup=m(g-a)Unit 5 (Dynamics) Equations:Momentum and Impulse:p=m?vpbefore=p'afterImpulse=F??tImpulse= ?p=p2-p1=m??vEnergy:EK=12mv2Ep=mghEK1+EP1=E'K2+E'P2Work and Power:W=F?d?cosθP=Wt=?EtW=?EK=EK2-EK1P=F?dt=F?vUnit 6 (Waves) Equations:Mechanical Waves:f=1Tv=λTv=fλSound Waves:vsound=331+0.6T λobserver=vsound±vsourcefsourcedB=10logIIofobserver=vsoundvsound±vsourcefsourceStanding Waves:L=n?λ2L=n?λ4L=λ2L=λ4Light Waves:n1sinθ1=n2sinθ2 ................
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