Name____________________________________ Section___________University of MarylandDepartment of PhysicsPhysics 122 Dr. David NoyesExam 1 Instructions:Do not open this examination until the proctor tells you to begin. Read these instructions whilewaiting.1. When the proctor tells you to begin, write your name and section number at the top ofevery page. 2. Do your work for each problem on the page for that problem. I will pass around paper so youcan do your scratch work on it before starting to write out your answer on the exam. If part ofyour answer is on the back, be sure to check the box on the bottom of the page so thegrader knows to look on the back!3. Partial credit will be granted for correct steps shown, even if the final answer is wrong. So besure to show your work.4. Write clearly and logically so I can understand what you are doing and can give you as muchpartial credit as you deserve. I cannot give credit for what you are thinking — only for what youshow on your paper.5. If on a multi-step problem you can't do a particular part, don't give up. Go on to the next partanyway. If necessary, define a name for the quantity you couldn't find and express youranswer in terms of it.6. You are not permitted to have any outside information during this exam. This includes anywritten information and any relevant information programmed into a calculator. If you arecaught using such information, you will be prosecuted and may receive a grade of XF for thiscourse. 7. If there is a formula or constant that is not given, but you think is needed, ask me and ifreasonable, I will put it on the board. However I will not tell you which equation is needed fora given problem. Also note that some of the formulas that are given only apply in certainsituations, so be sure to take that into account.8. Take a deep breath, relax, and good luck!Name____________________________________ Section___________Vibrations and Waves (27 points)1) (5 points) A mass attached to a spring oscillates back and forth as indicated in the position vs.time plot below. At point P, the mass has:a. Positive velocity and positive acceleration.b. Positive velocity and negative acceleration.c. Positive velocity and zero acceleration.d. Negative velocity and positive acceleration.e. Negative velocity and negative acceleration.f. Negative velocity and zero acceleration.g. Zero velocity but is accelerating (positively or negatively).h. Zero velocity and zero acceleration.2) (5 points) A mass suspended from a spring is oscillating up and down as indicated. Considertwo possibilities:(i) At some point during the oscillation the mass has zero velocity but is accelerating(positively or negatively).(ii) At some point during the oscillation the mass has zero velocity and zero acceleration.a. Both occur sometime during the oscillation.b. Neither occurs during the oscillation.c. Only (i) occurs.d. Only (ii) occurs.Name____________________________________ Section___________3) (5 points) A wave pulse is moving, as illustrated, with uniform speed v along a rope. Whichof the graphs below (A or B) correctly shows the relation between the displacement s of point Pand time t? A) B) 4) (12 points) Assume that a wave pulse traveling on a spring is described at time t = 0 as:y(x, t = 0) = 5 cm 5m<x<10my(x, t = 0) = 0 for all other values of xa) (3 points) Construct a graph below that portrays the actual shape of the spring at t=0.Be sure to label the graph.Name____________________________________ Section___________b) (3 points) If the pulse is traveling to the right with a velocity of 1 m/s, draw the shapeof the spring at time t = 2 s. Again be sure to label everything. c) (3 points) If the spring that wave pulse is traveling on has a linear mass density of 0.05kg/m, what is the tension in the spring?d) (3 points) Describe what you could do to increase the speed of the wave pulse. Electric Fields and Forces (28 points)5) (5 points) Three pithballs are suspended from thin threads. Various objects are then rubbedagainst other objects (nylon against silk, glass against polyester, etc.) and each of the pithballs ischarged by touching them with one of these objects. It is found that pithballs 1 and 2 repel eachother and that pithballs 2 and 3 repel each other. From this we can conclude that:a. 1 and 3 carry charges of opposite sign.b. 1 and 3 carry charges of equal sign.c. All three carry the charges of the same sign.d. One of the objects carries no charge.e. We need to do more experiments to determine the sign of the charges.Name____________________________________ Section___________6) (5 points) Two uniformly charged spheres are firmly fastened to and electrically insulatedfrom frictionless pucks on an air table. The charge on sphere 2 is three times the charge onsphere 1. Which of the 7 force diagrams correctly shows the magnitude and direction of theelectrostatic forces? Explain your reasoning.Name____________________________________ Section___________7) (6 points) In the figure at the left is shown a fixedcharge (specified by a circle) and a location (specifiedby the x). A test charge is placed at the x in order tomeasure the electric effect of the fixed charge. Complete the two statements below as quantitatively asyou can. (For example, if the result is larger by a factorof three don't say “increases” say “triples” or “ismultiplied by three”.) Each statement is meant to becompared with the original situation. (The changes don'tcumulate.)a. (3 points) If the test charge is replaced by one with half the amount of charge, then theelectric field it sees will _______ b. (3 points)If the fixed charge is replaced by one with twice the amount of charge, then theelectric field seen by the test charge will _______ 8) (12 points) For the charge configuration shown below q1 = 1nC, q2 = 5nC. Assume that q1and q2 are held in place and cannot move.Name____________________________________ Section___________a) (3 points) Find the electric field (magnitude and direction) at the point X, whosecoordinates are (x,y) = (1.5m, 4m). b) (3 points) If a charge q0 = 1nC was placed at the point X, what would the magnitudeand direction of the Coulomb force on this charge be?c) (3 points) Qualitatively describe the motion of q0 if it was placed at X and the chargesq1 and q2 are still fixed in place. d) (3 points) If instead of placing q0 at exactly (x,y) = (1.5m,4m) it was placed at (x,y) = (1.5 m, 3.9 m), how would the motion of q0 be
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