
Mechanics Free Response Question #3 Solutions  AP Physics C 1998 Released Exam
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This Free Response Question includes the following concepts: Free Body Diagrams (or Force Diagrams), Static and Kinetic Friction, Tension, Force Normal, Force of Gravity, Newton’s Second Law (many times), a Multiple Bock System and a Pulley.
AP® is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this product. Link: AP Physics C 1998 Released Exam The problem is on pages 159  161 of this pdf. Their solution is on pages 191  193 of this pdf. Please enjoy my solutions as well. Content Times: 0:22 Describing the Problem 1:24 Part (a) Drawing the Free Body Diagrams of the Whole System 1:58 Part (a) Forces of Gravity (or Weights) 2:22 Part (a) Tension Forces 2:53 Part (a) Normal Forces 4:06 Part (a) Friction Force(s) 4:56 Answering Part (a i) through (a v) 6:02 Part (b) 1st Net Force Equation 7:22 Part (b) 2nd Net Force Equation 8:20 Part (b) 3rd Net Force Equation 10:35 Part (c) Describing this part of the Problem 12:19 Part (c) The only Net Force Equation for Part (c) 14:37 Part (d) 15:29 Part (d i) 16:27 Part (d ii) 

I made a video called, “8 General Suggestions for the Free Response Questions of any AP Physics Exam.” And then I proceeded to make video solutions to the 3 Free Response Questions of the 1998 AP Physics C Mechanics Exam and I learned a valuable lesson. I should have given 9 suggestions. I should have added a 9th suggestion: “Read Carefully.”
I find it quite funny that I didn’t read carefully enough because (1) for years it is something I berated my students about and (2) it is something I did not do on the third free response question. You see, I didn’t answer part (a) completely. I missed the small word “magnitude”. I simply drew the forces in the Free Body Diagrams, however, I didn’t explicitly solve for the Magnitudes of the Forces. All the magnitudes of the forces are in my solutions because I had to find each one to solve the rest of the problem; however, I didn’t quite answer part (a) correctly. I did put the complete solution in my solutions. :)
I don’t know how the AP graders would grade my solution because all the physics is there, just not in the right places; however, I do feel they would not have given my solution full credit. So, please learn from my mistake and read the questions carefully. Don’t have to eat humble pie, like me.
I find it quite funny that I didn’t read carefully enough because (1) for years it is something I berated my students about and (2) it is something I did not do on the third free response question. You see, I didn’t answer part (a) completely. I missed the small word “magnitude”. I simply drew the forces in the Free Body Diagrams, however, I didn’t explicitly solve for the Magnitudes of the Forces. All the magnitudes of the forces are in my solutions because I had to find each one to solve the rest of the problem; however, I didn’t quite answer part (a) correctly. I did put the complete solution in my solutions. :)
I don’t know how the AP graders would grade my solution because all the physics is there, just not in the right places; however, I do feel they would not have given my solution full credit. So, please learn from my mistake and read the questions carefully. Don’t have to eat humble pie, like me.
