Syllabus Updated 2/13/2018 9:18 pm
Mastering Physics class ID: MPDANIELS34418, University Physics, 13e
Instead of taking off for incorrect answers, I am giving credit for correct answers up to a possible 120%. This should help anyone who was a “late bloomer.” Unfortunately, what is hurting most of you who are not doing well on the finals is simple algebra. If you know that you are weak in this area, then I encourage you to revisit algebra because it is completely essential to have fully mastered algebra in order to succeed in physics. (Don’t forget: the easiest way to check your work is to check your units. If you don’t know what that means or how to do it, find out.)
STEM Center Tutor Schedule Spring 2018 Updated 4/3/2018 4:16 pm
In addition to the homework, I recommend that you do as many example problems in the book and problems from the end of each chapter as you can.
Solving physics problems on your own is necessary to be able to learn physics.
Exam #1 Review Answers:
Equilibrium Problems Problem 4 is extra credit. Turn it in by the final. Do not ask for help.
*Number 5 Part d should say up. It was a Freudian slip.
*2. b. Plug in the second mass to obtain the final speed of the second body after the collision (5/4 v1).
*3. I mentioned during the exam that you could assume the initial angular speed was given. There is a “typo” in my written answer for part c. It should say omega(subscript one), not omega(prime).
I am still grading Exam #3, and I feel compelled to address some concerns:
I do not feel comfortable passing any student who cannot successfully solve a system of equations (algebra prerequisite), solve right triangles (trigonometry prerequisite), analyze vectors (Chapter 1), or evaluate forces (Chapter 4). Most of the physics is done when analyzing forces in problems which involve forces (including energy, work, rotational motion, torque, gravity, and equilibrium)! Additionally, anyone who has not mastered the concepts listed in the review packets I have provided will likely not receive an A because these are the fundamental concepts of this course, and understanding them are necessary to solving the problems (the only way to demonstrate knowledge and understanding in physics). It is not simply enough to know the equations; you must be able to use them. You must understand what each equation (and each letter in the equation) physically represents and be able to translate it to the problem and vice versa. You should also know the derivation for each equation or at least understand where it comes from. You should NEVER use an equation if you do not know how you know it is correct and applicable, which you cannot know if you have not proved it yourself. This class requires active and purposeful critical thinking, not passive gratuitous memorization. Your future physics classes will require you to know everything covered in these review packets at the bare minimum.
Regarding drawing forces and free-body diagrams, there are really only seven forces that we covered in total (1. the normal force, 2. weight, 3. friction, 4. air resistance, 5. tension, 6. the spring force, and 7. applied forces), and we usually only deal with four or five at most at a time. When looking at forces, only look at ONE object at a time, both for the free-body diagram AND for the sum of force equations (and review the definition of a system and how to treat one). When drawing a free-body diagram only consider forces acting ON the object of interest. Do NOT combine the x- and y-components of force in the same force equation unless you are expressly writing them as vectors, in which case you must still add the vectors correctly (Chapter 1)! Understand when objects do not have the same mass and/or acceleration and whether or not they are accelerating, and approach them accordingly EVERY SINGLE TIME (Newton’s second law)! Here is a quick summary of each force: 1. The normal force is present when there is contact between two surfaces and is perpendicular to each surface (equal and opposite: Newton’s third law) and goes through the object of interest (away from the surface). 2. Weight is present when an object with mass is in a gravitational field (in this course it is usually that of Earth at its surface) unless otherwise indicated to be negligible (or due to some other gravitational field or at some other distance from Earth’s center of mass). The reaction force to weight is the force with which the object pulls on Earth. The weight vector goes from the center of mass of an object and points down to Earth’s center of mass. If you are negotiating an inclined plane, you will usually turn your coordinate system so that weight is the only (or one of the only) force(s) that you need to split into components. Do not change the actual forces just because you are changing the coordinate system. Find the angle that the weight makes with your new coordinate system and solve that right triangle when splitting your components. 3. Friction is always parallel to the surface and opposes the motion, but you have to recognize what that means for each object. For example, friction is in the same direction of your acceleration if it is causing the acceleration. The frictional force is equal to the coefficient of friction times the normal force which applies to the friction. You do not always need to write the friction this way, but you definitely need to know the difference between the force of friction and the coefficient of friction (which is a unitless number). Always check your units (which means you have to know the units). 4. Air resistance is similar to friction, but I will not test you on it. 5. Tension ALWAYS points AWAY from the object of interest (you cannot push a rope) along the rope/string/cable/etc… The reaction force to tension is the equal and opposite tension on the other side of the rope/string/cable/etc… When dealing with torque (massive pulleys or otherwise) the tension on either side of the pulley is not equal if it is causing torque, but the previous statement still applies on each separate side. 6. The spring force is parallel to the motion of the spring and in the opposite direction of the displacement (Hooke’s law). 7. Applied forces are usually indicated by an arrow or explained in words. This is typically due to a hand pushing or pulling but may not always be explained other than as a force. Additionally, pay attention to variables and subscripts.
I want to acknowledge that you all did a much better job at keeping things simple and “following the recipe” on Exam #3, but please make sure to review the above concepts before the final. You can do this.
Final Solutions *There were two versions of the final. These solutions contain the answers for both versions. There are some errors in these solutions. There was an algebra error on the rolling sphere on the inclined plane problem. 1/2 + 1/3 = 5/6. For the pulley system problem, I forgot to include friction, and the acceleration used in finding the time to hit the floor should not be the acceleration due to gravity. I have posted the correct solutions below.
Final Equation Sheet You will need to know how to find the moment of inertia of a collection on particles, the parallel axis theorem and how to use it, and all equations for the last two chapters, except for: black holes; angular simple harmonic motion; damped oscillations; forced oscillations; or resonance. The more equations I give you the more difficult I can make the exam. You can derive most of the equations from the equations I will give you. I recommend doing the example problems in the chapters, at least one problem from each section in the back of the chapters, and as many “Problems” questions in the back of the chapters as you can in addition to the homework. You should also practice the problems we did in class, and I will post some more practice problems over the weekend. Good luck!
Practice Problems (Chapters 13 & 14) These problems are very simple and meant to help you with the concepts. Be prepared to use your critical thinking on the second half of the final. You can do it.
Practice Problems (Chapters 13 & 14) Solutions *8. d. is incorrect because the system begins with an initial velocity. The corrected solution is posted below:
Carnegie Rule: The Carnegie rule is a rule of thumb suggesting how much outside-of-classroom study time is required to succeed in an average college course. Typically the Carnegie Rule is reported as two to three hours of outside work required for each hour spent in the classroom.