MSU EGR 100 - 07newtons3rdlaw (43 pages)

Chapter 7 Newton s Third Law Topics Interacting Objects Analyzing Interacting Objects Newton s Third Law Ropes and Pulleys Examples of Interacting Object Problems Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Chapter 7 Reading Quizzes Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley The propulsion force on a car is due to A static friction B kinetic friction C the car engine D elastic energy Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Is the tension in rope 2 greater than less than or equal to the tension in rope 1 A greater than rope 2 B less than rope 2 C equal to rope 2 Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley An acceleration constraint says that in some circumstances A the acceleration of an object has to be positive B two objects have to accelerate in the same C the magnitude of the accelerations of two objects have to be equal D an object is prevented from accelerating E Acceleration constraints were not discussed in this chapter Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Interacting Objects If object A exerts a force on object B then object B exerts a force on object A The pair of forces as shown is called an action reaction pair Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Interactions through Contact at a Distance Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Car B is stopped for a red light Car A which has the same mass as car B doesn t see the red light and runs into the back of B Which of the following statements is true A A exerts a larger force on B than B exerts on A B A exerts a force on B but B doesn t exert a force on A C B exerts a force on A but A doesn t exert a force on B D B exerts a larger force on A than A exerts on B E B exerts the same amount of force on A as A exerts on B Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley A small car is pushing a larger truck that has a dead battery The mass of the truck is larger than the mass of the car Which of the following statements is true A The truck exerts a larger force on the car than the car exerts on the truck B The truck exerts a force on the car but the car doesn t exert a force on the truck C The car exerts a force on the truck but the truck doesn t exert a force on the car D The car exerts a larger force on the truck than the truck exerts on the car E The car exerts the same amount of force on the truck as the truck exerts on the car Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Applications Acceleration Constraints Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Acceleration Constraint in Action If the rope is pulled down10 cm how far up does the 10 2 kg mass move Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Applications Strings and Pulleys Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Tension another look Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley The Massless String Approximation Often in physics and engineering problems the mass of the string or rope is much less than the masses of the objects that it connects In such cases we can adopt the following massless string approximation Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley All three 50 kg blocks are at rest Is the tension in rope 2 greater than less than or equal to the tension in rope 1 A Equal to B Greater than C Less than Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Tactics Analyzing interacting objects Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Tactics Analyzing interacting objects Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Tactics Analyzing interacting objects Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley What s in your system vs the environment Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley INTERACTION DIAGRAMS FREE BODY DIAGRAMS Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Problem Solving Strategy InteractingObjects Problems Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Problem Solving Strategy InteractingObjects Problems Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley A fishing line of negligible mass lifts a fish upward at constant speed The line and the fish are the system the fishing pole is part of the environment What if anything is wrong with the free body diagrams A The force of the pole on the fish is missing B The force of gravity on the line is missing C The gravitational force and the tension force are incorrectly identified as an action reaction pair D There should be only one force on the fish E There is nothing wrong with the free body diagrams Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley EXAMPLE 7 3 The forces on accelerating boxes Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley EXAMPLE 7 3 The forces on accelerating boxes Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley EXAMPLE 7 3 The forces on accelerating boxes Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley Boxes A and B are sliding to the right across a frictionless table The hand H is slowing them down The mass of A is larger than the mass of B Rank in order from largest to smallest the horizontal forces on A B and H A FH on B FH on A FA on B B FB on H FH on B FA on B FB on A C FB on H FH on B FA on B FB on A D FB on H FH on B FA on B FB on A Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley In the figure to the right is the tension in the string greater than less than or equal to the weight of block B A Equal to B Greater than C Less than Copyright 2008 Pearson Education Inc publishing as Pearson Addison Wesley EXAMPLE 7 6 Comparing two tensions QUESTION