Name__________________________________ Section ___________ University of Maryland Department of Physics Physics 121 Dr. E. F. Redish Fall 2007 Exam 1 12. October, 2007 *** Good Luck *** Instructions: Do not open this examination until the proctor tells you to begin. 1. When the proctor tells you to begin, write your full name and section number at the top of every page. This is essential since this exam booklet will be separated for grading. 2. Do your work for each problem on the page for that problem. You might find it convenient to either do your scratch work on the back of the page before starting to write out your answer or to continue your answer on the back. If part of your answer is on the back, be sure to check the box on the bottom of the page so the grader knows to look on the back! 3. On all the problems except the multiple choice questions in problem 1 or where it says not to explain, your answers will be evaluated at least in part on how you got them. If explanations are requested, more than half the credit of the problem will be given for the explanation. LITTLE OR NO CREDIT MAY BE EARNED FOR ANSWERS THAT DO NOT SHOW HOW YOU GOT THEM. Partial credit will be granted for correct steps shown, even if the final answer is wrong. 4. Write clearly and logically so we can understand what you are doing and can give you as much partial credit as you deserve. We cannot give credit for what you are thinking — only for what you show on your paper. 5. All estimations should be done to the appropriate number of significant figures. 6. At the end of the exam, write and sign the honor pledge in the space below: “I pledge on my honor that I have not given or received any unauthorized assistance on this examination.” #1: #2: #3: #4: #5: TotalNAME_________________________SECTION___________POINTS_______ Physics 121 Dr. E. F. Redish Fall 2007 Exam 1 If you need more space, continue on the back and check here. 1. (30 points) A ball is launched up a ramp by a spring as shown in the figure at the right. At the time when the clock starts, the ball is near the bottom of the ramp and rolling up the ramp as shown. It goes to the top and then rolls back down. For the graphs shown below, the horizontal axis represents the time. The vertical axis is unspecified. For each of the following quantities, select the number of the graph that could provide a correct graph of the quantity for the ball in the situation shown (if the vertical axis were assigned the proper units). Use the x and y coordinates shown in the picture. If none of the graphs could work write N. (Note:“x component” of a vector means “the part of the vector in the x direction”.) (a) The x component of the ball’s position. _______ (b) The y-component of the ball’s velocity _______ (c) The x-component of the ball’s acceleration _______ (d) The y-component of the normal force the ramp exerts on the ball _______ (e) The x-component of the ball’s velocity _______NAME_________________________SECTION___________POINTS_______ Physics 121 Dr. E. F. Redish Fall 2007 Exam 1 If you need more space, continue on the back and check here. 2. (20 points) Two blocks are sitting on a spring scale as shown in the figure. The reading on the spring scale is equal to the force the spring is exerting upwards. You press downward on the block labeled B with a constant force as shown in the diagram. (a) In the boxes below, draw free body diagrams for the two blocks, labeling each force so as to identifying the character of the forces (N, T, f, or W), who is causing the force, and who is feeling the force. (10 pts) (b) Which pairs of forces in your diagram in part (a) have magnitudes equal to each other, if any? For each pair you specify, give the reason why you think they are equal. (5 pts) (c) Are there any equalities among combinations of forces in your diagrams in part (a) that you can identify? For each combination you specify, give the reason why you think the equality holds. (5 pts)NAME_________________________SECTION___________POINTS_______ Physics 121 Dr. E. F. Redish Fall 2007 Exam 1 If you need more space, continue on the back and check here. 3. (15 points) A standard media for distributing computer information these days is a CD that can hold about 800 MegaBytes (8 x 108 Bytes) of data. Given that one English character (letter, number, etc.) requires 1 Byte of storage space, estimate how many novels can be stored on a single CD. Be sure to clearly state your assumptions and how you came to the numbers you estimated, since grading on this problem will be mostly based on your reasoning, not on your answer.NAME_________________________SECTION___________POINTS_______ Physics 121 Dr. E. F. Redish Fall 2007 Exam 1 If you need more space, continue on the back and check here. 4. (10 points) So far in this class we have found by careful observation a number of results that we did not expect. In some cases, this was because our intuitions were focused on one changing factor but we ignored another important factor that also changed. Describe one example like that where your original intuition did not match the observation. Explain whether you were able to reconcile it your intuition with what you saw. If you were able to reconcile, explain how. If not, explain why not. (If your intuitions were always correct, explain how someone might have such an intuition and what they might do to reconcile.) Note: This is an essay question. Your answer will be judged not solely on its correctness, but for its depth, coherence, and clarity. ____________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________
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