Mastering Physics 2 Sample - Sciencepress

2MODULEDynamicsBrian Shadwick

Science Press 2020First published 2020Science PressUnit 7, 23-31 Bowden StreetAlexandria NSW 2015 AustraliaTel: 61 2 9020 1840 Fax: 61 2 9020 auAll rights reserved. No part of this publicationmay be reproduced, stored in a retrieval system,or transmitted in any form or by any means,electronic, mechanical, photocopying, recordingor otherwise, without the prior permission ofScience Press. ABN 98 000 073 861

ContentsWords to Watch ivForces2.1Forces, Equilibrium and Newton’s First Law2Types of forces Equilibrium and Newton’s first law 242.2/3 Forces In One and Two Dimensions 5Forces in one and two dimensions – vector revision 5Forces in two dimensions 1 6Forces in two dimensions 2 82.13Energy Transformations Near Earth’s Surface332.14Horizontal Blocks In Contact and Masses Connected By Strings35Horizontal blocks in contact Masses connected by strings – horizontal surfaceMasses connected by vertical strings 3537Momentum, Energy andSimple Systems2.15Force, Acceleration and Energy2.42.5Newton’s First Law Of Motion and Friction10Newton’s first law of motion and inertia The role of friction Coefficient of friction 101112Newton’s Second Law Of Motion 14Newton’s second law: F ma 14Newton’s second law – qualitative descriptions 152.6/7 Analysing Motion Experiments 2.162.17Impulse, Momentum and Road Safety 42Impulse and momentum Momentum and road safety 4244Colliding Objects 45Colliding objects 1 Colliding objects 2 Colliding objects 3 Colliding objects 4 45474849One-Dimensional Interactions Of Objects50Analyse experimental data – one dimension 502.18Two-Dimensional Interactions Of Objects52161819202.19Collisions In Two Dimensions 54Motion Of Objects On Inclined Planes 212.20Force-Time Graphs 55Force-time graphs Force and time in collisions 5557Analysing a motion experiment 1 Analysing a motion experiment 2 Analysing a motion experiment 3 Analysing motion 2.81639Analyse experimental data – two dimensions 52Analysing an experiment – inclined plane Motion on an inclined plane 21222.9Newton’s Third Law 242.10Work Done By Forces 252.11Force-Displacement Graphs 27Answers 612.12Power and Gravitational Potential Energy29Data Sheet 89Formula Sheet 90Power Gravitational potential energy 2931Periodic Table 91Science PressMASTERING PHYSICSISBN 978-0-85583-82182.21/22Elastic and Inelastic Collisions NSW Module 2Dynamics58iii

Words to Watchaccount, account for State reasons for, report on,explain Make something clear or easy to understand.give an account of, narrate a series of events orextract Choose relevant and/or appropriate details.transactions.analyse Interpret data to reach conclusions.annotate Add brief notes to a diagram or graph.apply Put to use in a particular situation.assess Make a judgement about the value ofsomething.calculate Find a numerical answer.clarify Make clear or plain.classify Arrange into classes, groups or categories.comment Give a judgement based on a givenstatement or result of a calculation.compare Estimate, measure or note how things areextrapolate Infer from what is known.hypothesise Suggest an explanation for a group offacts or phenomena.identify Recognise and name.interpret Draw meaning from.investigate Plan, inquire into and draw conclusionsabout.justify Support an argument or conclusion.label Add labels to a diagram.list Give a sequence of names or other brief answers.measure Find a value for a quantity.similar or different.outline Give a brief account or summary.construct Represent or develop in graphical form.plan Use strategies to develop a series of steps orcontrast Show how things are different or opposite.create Originate or bring into existence.deduce Reach a conclusion from given information.define Give the precise meaning of a word, phraseor physical quantity.demonstrate Show by example.derive Manipulate a mathematical relationship(s) togive a new equation or relationship.describe Give a detailed account.design Produce a plan, simulation or model.determine Find the only possible answer.discuss Talk or write about a topic, taking intoaccount different issues or ideas.distinguish Give differences between two or moreprocesses.predict Give an expected result.propose Put forward a plan or suggestion forconsideration or action.recall Present remembered ideas, facts orexperiences.relate Tell or report about happenings, events orcircumstances.represent Use words, images or symbols to conveymeaning.select Choose in preference to another or others.sequence Arrange in order.show Give the steps in a calculation or derivation.sketch Make a quick, rough drawing of something.different items.solve Work out the answer to a problem.draw Represent by means of pencil lines.state Give a specific name, value or other brief answer.estimate Find an approximate value for an unknownsuggest Put forward an idea for consideration.quantity.summarise Give a brief statement of the main points.evaluate Assess the implications and limitations.synthesise Combine various elements to make aexamine Inquire into.whole.ivNSW Module 2DynamicsScience PressMASTERING PHYSICSISBN 978-0-85583-8218

ForcesScience PressMASTERING PHYSICSISBN 978-0-85583-8218NSW Module 2Dynamics1

2.1 Forces, Equilibrium and Newton’s First LawUsing Newton’s laws of motion, describe static and dynamic interactions between two ormore objects and the changes that result from a contact force – a force mediated by fields.Types of forcesApplied forcesHitting a ball, punching a bag,kicking a ball, pushing a swing,opening a door, cutting bread,hammering a nail.Frictional forcesBetween tyres and the road,slowing you down on a slide,makes hands warm whenyou rub them together.Normal force RNormal forcesContactforcesForcesactingat adistance2NSW Module 2DynamicsW mgUpward force of floor on you asyou stand, of chair on you as yousit, on book resting on table, alsocalled reaction forces.Drag forcesAir resistance, slowing swimmersdown, why objects fall slowerthrough oil than through water,why there is terminal velocity.Tension forcesBending a ruler, stretching arubber band, pulling a bridge cabletight, twisting a bar, forces inropes, cables, strings and wires.Spring forcesIn springs that are compressed orstretched, act in opposite directionto the applied forces, compressionor tension forces.Magnetic forcesMagnetic field surrounds magnetsand electric currents, put magneticforces on charges. Like magneticpoles repel, unlike poles attract.Electrical forcesElectric fields surround chargesand apply forces to other charges.Like charges repel, unlike chargesattract.Gravitational forcesForce of attraction between allmasses in the Universe. Givesmasses weight and often calledweight force.Science PressMASTERING PHYSICSISBN 978-0-85583-8218

Sample1.QuestionsComplete the diagram.ALL FORCES2.Explain, in terms of forces, what the diagram on the right is showing.3.The diagram below shows three objects on top of each otheron a table.(a) On a copy of this diagram label four gravitational forcesand four normal forces.(b) Label each force.A4.BThe diagram shows the two different masses hanging on thesame spring.(a) Suggest a reason the spring is extended more in A thanin B.(b) Which spring will have the greater tension set up within it?Justify your answer.Science PressMASTERING PHYSICSISBN 978-0-85583-8218NSW Module 2Dynamics3

Equilibrium and Newton’s first law A body is said to be in equilibrium if it is at rest or if it is moving with uniform velocity.Note that being in equilibrium does not mean that no forces act.When two or more forces act on a body which is in equilibrium, the net force must be zero.There will be no acceleration, but the body may still move with constant velocity.The concept of equilibrium is the focus of Newton’s first law of motion.A body at rest, or moving with constant velocity, will remain at rest or moving with constantvelocity unless an unbalanced force acts on it.Types of equilibrium Static equilibrium exists if all the forces acting on a body add to zero, and the body is at rest. A folder resting on your desk. Your car parked in the school car park. A can of drink sitting on a shelf in the fridge are all in static equilibrium.Dynamic equilibrium exists if all the forces acting on a body add to zero, and the body is moving atconstant velocity. A car moving at constant speed. A parachute jumper falling towards the ground at constant (terminal) velocity. A comet moving through space at constant velocity are all in dynamic equilibrium.SampleQuestions1.State the conditions needed for translational equilibrium.2.Explain the idea of static equilibrium.3.Explain the idea of dynamic equilibrium.4.Identify these as being in static or dynamic equilibriumor as not being in equilibrium.(a) Light fitting hanging from the ceiling.(b) Ski jumper moving down the slope towards thejumping ramp.(c) Plane taking off.(d) A computer on your desk.(e) Tree branches swaying in the wind.(f) Mudslide down the side of a hill.(g) Apollo 11 coasting between the Earth and theMoon.(h) Arrow poised in bow ready to fire.(i)Car travelling at constant speed up hill.(j)Car travelling at constant speed on flat road.(k) Car travelling at constant speed down hill.4NSW Module 2DynamicsAt the moment the ball at the top of thismechanical maze is in static equilibrium – but touch it and the equilibrium might be lost.Science PressMASTERING PHYSICSISBN 978-0-85583-8218

2.2/3 Forces In One and Two DimensionsExplore the concept of net force and equilibrium in one-dimensional and two-dimensionalcontexts using algebraic addition, vector addition and vector addition by resolution into components.Apply the following relationships, solve problems or make quantitative predictionsabout resultant and component forces using Fx F cos θ and Fy F sin θ.Forces in one and two dimensions – vector revision Forces are vector quantities and can therefore be represented by scale diagrams.Force is measured in newtons, symbol N.SampleQuestionsRefresh your skills by doing thequestions below which refer tothe force vectors in the diagram.The vectors have been drawnusing a scale where 1 cm 10 N.In answering the questions, makeall measurements to the nearest0.5 cm. Give all directions asbearings to the nearest degree.1.A B11. G D2.C D12. K C3.E F13. I B4.G–B14. L – A5.D H15. D J6.E–K16. G 2J7.A C E17. M C8.I J K18. I A9.E F–D19. K B10. M – L – H20. L EABGHIJCDEKNFLMScience PressMASTERING PHYSICSISBN 978-0-85583-8218NSW Module 2Dynamics5

Forces in two dimensions 1 Like all vector quantities, forces can be resolved into two perpendicular components in the x and ydirections.The two force components are given by the equations:Fx F cos θyyFy F sin θFFFy F sin θθθxOSampleOxFx F cos θQuestionsEach of the following diagrams show masses in static equilibrium. Using your knowledge of components ofvectors, analyse each situation to determine the unknown quantities.1.A mass of 25 kg hangs on a string whichis pulled to the side by force F until thestring makes an angle of 32 to thevertical.(a) What is the force pulling thesupporting string to the side?(b) What is the tension in the rope?32 TensionForcem 25 kg2.6The diagram shows the forces actingon a 15 kg mass on a smooth surface.(a) Calculate the resultant force on theobject.(b) What will be its acceleration?(c) How fast will it be going after 2.5 s?(d) Calculate the normal reaction forceof the surface on the mass.NSW Module 2Dynamics164 N55 N15 kg30 Science PressMASTERING PHYSICSISBN 978-0-85583-8218