General Physics PHY 007B
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This 4 page Class Notes was uploaded by Horace McClure on Tuesday September 8, 2015. The Class Notes belongs to PHY 007B at University of California - Davis taught by John Conway in Fall. Since its upload, it has received 329 views. For similar materials see /class/191835/phy-007b-university-of-california-davis in Physics 2 at University of California - Davis.
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Date Created: 09/08/15
Physics 7B DLM 4 Overview Unit 4 Momentum and Force ModelApproach Momentum Conservation Model Act 424 Momentum and Change in Momentum in Two and Three Dimensions 11 70 min FNTs 1 6 from DLM 3 Learning Goals 39 Get practice identifying momentum and change in momentum in two and three dimensions 39 Get practice identifying impulse from the net force in multiples spatial dimensions 39 Get practice representing impulse momentum and change in momentum as vectors using scaledarrows in momentum charts 39 Get practice defining and analyzing phenomena that occur in more than one dimension using momentum charts to facilitate using the Momentum Conservation Model Act 425 The Importance of At in Collisions 70 min Tablecloth activity and FNTs 7 10 from DLM 3 Learning Goals 39 Get practice defining and analyzing phenomena using momentum charts to facilitate using the Momentum Conservation Model Develop an intuitive understanding of how At affects net Impulse J and net force SF in collisions and the tablecloth trick Get practice making meaningful estimates of At and SF in automobile crashes Announcements 39 Reading Assignment Finish reading Unit 4 39 Be sure to use the Physics 7B webpage periodically for new information and material and practice problems Physics 7B DLM4 Exit Handout DLM 04 FNTs 1 6 Two asteroids collide headon and stick together Before the collision asteroid A mass 1000 kg moved at 100 ms and asteroid B mass 2000 kg moved at 80 ms in the opposite direction Use momentum conservation make a complete Momentum Chart to nd the velocity of the asteroids after the collision Two asteroids identical to those in FNT l collide at right angles and stick together ie their initial velocities were perpendicular to each other Use momentum conservation make a complete Momentum Chart to nd the velocity magnitude and direction withrespectto the velocity asteroid A had before the collision of the asteroids after the collision Determine the fractional decrease in total kinetic energy of the two asteroids in the previous two FNTs when they collide If the average speci c heat of the material composing the asteroids is assumed to be that of ice 205 ldkgC by how much does the temperature of the asteroids rise as a result of the collision in each case Throw an object like a ball horizontally and observe its motion You are now going to analyze this motion using conservation of momentum Consider the motion of the ball just after it has left your hand moving in a horizontal direction a Draw a force diagram for the ball What direction is the net force b Complete the first two rows in the given momentum chart The pi of each successive step will be the pf from the previous step What direction is Ap 0 Add three more rows to the Momentum Charts just show the three vectors pi Ap and pf Assume the same time interval for each change such that Ap will be 15 the length of the initial momentum pi Open d Why does Ap stay constant for each step SyStem Pi AP Pf 6 After you have carefully constructed a series Ball Atl I of final momenta use them and what you 5 know about the relationship of the direction B an Atz of momentum to the path of an object to construct a path of the ball Repeat what you did in FNT 4 but this time do two separate momentum charts for the horizontal and the vertical components of the motion Describe in words how the motion changes in the two directions Compare your diagrams from part 6 between 4 amp 5 Are the paths you constructed still the same a Wrap up what you have done in questions 4 and 5 by explaining in as few words as possible why the ball moves in this path b For any object to be moving in a curved path what is necessary about the relationships pi Ap pf and 2F c If Ap were always perpendicular to pi and pf what type of path would this be thsics 7B DL Activitv 424 DLM 04 Momentum and Change in Momentum In Two and Three Dimensions 11 1 FNT 1 DLM 3 heavy ball swung in a horizontal circle string breaks a On the board draw a physical picture of the situation Make sure to include from 10 before the string breaks until the alter the string breaks b Make a momentum chart for this phenomenon taking the initial point to be about 10 before the string breaks and the nal point to be immediately before the string breaks c On the board make a second momentum chart for this phenomenon taking the initial point to be immediately after the string breaks and the nal point to be after the ball has gone a short distance d Use your charts to explain the path of the heavy ball both before and after the string breaks 2 FNT 2 DLM 3 puck moving in a straight line receives a kick at right angles a On the board make a momentum chart for this phenomenon taking the initial point to be just before the kick and the nal point to be just after the kick b V On the board make a second momentum chart for this phenomenon taking the initial point to be the same point as the nal point in 2a and the final point to be after the puck has traveled some distance c Use your momentum charts to explain the path of the puck d V Considering your work above in 2a what is the predominant effect of the kick 3 FNT 3 DLM 3 puck moving in a straight line receives a kick at light angles On the board use the appropriate momentum chart from 2 to justify your answer to FNT 3 4 FNT 4 DLM 3 puck moving in a straight line receives a kick at right angles On the board use the appropriate momentum chart from 2 to make a scaled force diagram to answer FNT 4 5 FNT 5 DLM 3 ball dropped and bounces On the board make a momentum chart include a force diagram that helps make sense of this situation and helps you to answer the question in FNT 5 thsics 7B DL ActivitV 425 The Importance of At in Collisions DLM 04 Phenomenon These FNTs and the next activityipulling a tablecloth out from under the dishes7 illustrate how the time duration of an impulse relates to the net force and Ap A FNTs 6 7 and 8 DLM 3 Automobile crash 1 2 In your group decide on two specific scenarios FNT 8 and use these scenarios below in parts 2 3 and 4 to answer all of the other questions in this set of FNTs On the board put up complete momentum charts with force diagrams and equations worked through to numerical values for the car and for the person in each of the two scenarios you have chosen Describe the scenario above each of the momentum charts for the person Use your momentum charts to explain why the net force acting on the person will not be the same in both scenarios For each of the scenarios that you described in FNT 8 you will estimate the magnitude of the average force that would have been acting on you to bring you to a stop i You will have to determine the time during which the impulse acts for the different scenarios To do this you must first decide the initial and final momentum for the cases you are describing and over what distance does the impulse act ii Now you need to calculate the time of the impulse using your knowledge of how distance and time are related If you assume that you slow down at a constant rate then your average speed during this time is one half your initial speed iii Make an estimation of the average force for the two situations If your answers differ for the situations explain what factor is causes this difference If you know the initial and the final momentum then you know the impulse In each of your scenarios did you have the same or a different impulse What then is the effect of changing At with the given constraints in the case of this automobile crash Whole class sharing
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