# UMass Amherst PHYSICS 131 - Experiment 4 131 (4 pages)

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## Experiment 4 131

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- School:
- University of Massachusetts Amherst
- Course:
- Physics 131 - Intro Physics I

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Conservation Lab Physics 131 Section L Thursdays 9 00 AM ILC S110 6 22 17 Abstract Newton s third law describes the conservation of momentum about how every action has an equal reaction which can be seen in the PAScar system to elastic collision when the momentum and energy upon release of one car is equal to that of the two cars after a collision Along with the loss of kinetic energy when two separate objects are collided forming one system in the inelastic experiment Questions Answers 1 In case of elastic collisions what would happen if m1 is much much larger than m2 Conversely what would happen if m1 is much much smaller than m2 2 points When m1 is much much larger than m2 it s velocity is slowed after the collision but it continues moving in the same direction it was released in while if m1 is much much smaller than m2 after the collision it is moved in the opposite direction of where it was originally traveling 2 In your lab manual the equations 4 4 and 4 5 give the final velocities of the two objects in terms of the initial velocity and the masses Now are the final velocities you found in your trials consistent with these equations Show your work 2 points Table 1 Data assortment of masses velocity KE and P of trials Equation 4 4 0 28 0 500 Equation 4 5 22 2 28 250 500 Doesn t work our results show that V2 28 the equation says V2 22 Our results for equation 4 4 are in line with what the equation says we should have gotten 0 and our results equal 0 However for equation 4 5 the equation shows we should have gotten 22 for V2 but our results show our V2 as being 22 3 Using the velocities make a TABLE for the momentum and kinetic energy of each PAScar before and after collision Calculate the percent difference between TOTAL final and initial momenta and kinetic energy in each trial and comment on the conservation of momentum and conservation of energy 2 points Mass proportion P before g m s P after g m s Percent difference Pbefore Pafter Pb efore 100 m1 m2 elastic 70 55 21 42 m1 m2 elastic 200 180 10 m1 m2 elastic 120 115 4 1 m1 m2 inelastic 105 5 80 21 95 Mass proportion KE before J KE after J Percent difference KEbefore KEafter KEbefore 100 m1 m2 elastic 19 6 12 1 38 26 m1 m2 elastic 80 61 35 23 31 m1 m2 elastic 57 6 41 7 27 6 m1 m2 inelastic 42 025 12 8 69 5 4 In the inelastic collision why do you need to measure only one final velocity 2 points You only measure one final velocity because the cars are stuck together making them one unit travelling at the same velocity so there is only one because the two cars can t travel at different rates while stuck together 5 In the inelastic collision why do you think the kinetic energy is not conserved 2 points Kinetic energy is not conserved because unlike momentum energy in scalar This means that the energy can be transferred to different forms such as released as heat so not all the energy from the collision will remain as energy in the car i e some can be released as heat so that is why you see the difference in kinetic energy because while the same amount of total energy is conserved the type of energy it is can change from kinetic to a different form 6 What physical law s predicts the conservation of momentum Explain briefly and clearly 2 points Newton s third law predicts the conservation of momentum As every action has an equal and opposite reaction which means the momentum of action will be conserved and same amount with happen before and after an event occurs The law of conservation of momentum states that in an isolated system the momentum of a collusion between Object1 and Object2 will be equal to each other 7 In the case of inelastic collisions what would happen if m1 is much much larger than m2 Conversely what would happen if m1 is much much smaller than m2 2 points In the case of inelastic collisions two objects stick together going from two separate objects to one whole unit Kinetic energy is lost possible as heat or other forms of energy V12 from the table is the final velocity of the system Assuming that v0 remains the same for the moving mass if m1 is much larger than M2 v12 will have a greater value than when m2 greater than m1 8 Imagine the PAScars m1 and m2 are both on the track at rest and with their bumpers touching each other The mass m1 2 m2 A firecracker is placed between the bumpers and explodes sending the PAScars in opposite directions What was the initial momentum of the system before the explosion What can you say about the final momentum of the system 2 points The initial momentum of the system because it is at rest is 0 The final momentum of the system is also zero since the two cars will have the same momentum in opposite directions Their velocities however will most likely differ Conclusion Although it is possible for the two cars to have different velocities and masses the momentum between the two upon collusion is preserved regardless of the masses while the direction of movement and speed of the two cars can differ based on the masses the momentum will remain balanced before and after the collision If the two cars are apart of the elastic reaction kinetic energy will also be preserved however if the cars form one unit in the inelastic reaction the kinetic energy will decrease as some of the energy will be lossed to other forms

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