FAMILY NAME Given Name(s) Student Number Practical Group as on student card as on student card Code

Transcription

1 FAMILY NAME Given Name(s) Student Number Practical Group as on student card as on student card Code PHY131H1F Term Test 2 version A Tuesday, November 19, 2013 Duration: 80 minutes Aids allowed: A pocket calculator with no communication ability. A single aid-sheet prepared by the student, no larger than 8.5 x11, written on both sides. A hard-copy English translation dictionary. Completely turn off any communication device you may have and leave it with your belongings at the front of the room. DO NOT separate the sheets of your question paper. You can, however, carefully tear off the blank page at the end, as it does not have to be handed in. Before starting, please PRINT IN BLOCK LETTERS your name, student number, and practical group code at the top of this page and on the answer sheet. Locate your test version number in the header at the top of the this page, and fill in the circle with the corresponding version code on your answer sheet in the Form Code box. Mark in your student number by shading the circles at the top-right of the sheet, starting with a 0 if the first digit is a 9. It is not required to bubble in your surname on the lower half of the sheet. Scanned Area of the reverse side of the Answer Sheet: 1. Use a dark-black, soft-lead pencil or a black pen. 2. Indicate your answer to a multiple-choice question by thoroughly filling the appropriate circle on the answer sheet and also by recording your answer on the test paper. 3. If you wish to modify an answer, erase your pencil mark thoroughly, or use dry tape white-out sparingly. 4. Do not write anything else on the answer sheet. Use the blank sheets at the end or the back of the question sheets for rough work. The test consists of 8 multiple-choice questions, worth 3 points each, or altogether 24 points. The test also has a set of free-form questions worth 16 points, for which fully worked solutions are required. The total possible number of points is 40. Multiple-choice questions: Please choose the best answer. Blank or incorrect answers are worth zero points. Multiple answers for the same question result in zero points for that question. Free-form Questions: To be awarded maximum credit, you must provide fully worked solutions to all parts of the free-form questions. In addition to showing your work, please put your answer(s) for each part in the boxes provided. You can use the back-side of the sheets and the blank pages at the end for your rough work which will not be graded or taken into account. When the invigilators declare the test ended, stop any writing or filling of circles on the answer sheet immediately. Please put your answer sheet inside your test paper and have the paper ready for an invigilator to pick up. Page 1 of 6

2 Possibly helpful information for this test: π = is the ratio of the circumference to the diameter of a circle g = 9.80 m/s 2 is the acceleration due to gravity near the Earth s surface. Common Prefixes: k = kilo- = 10 3 c = centi- = 10 2 m = milli- = 10 3 μ = micro- = 10 6 n = nano- = 10 9 The quadratic equation: If ax 2 + bx + c = 0, then x b b2 4ac 2a Air resistance may be neglected in all questions. MULTIPLE CHOICE (24 points total) Question 1 A 70.0 kg person steps onto an elevator to find a 10.0 kg box resting on a scale. While riding in the elevator, the person notices that the scale reads 11.0 kg with the box on top of it. At this moment, what is the magnitude of the force N on the person from the elevator floor? You may assume that she stands still relative to the floor. (a) 617 N (b) 686 N (c) 739 N (d) 755 N (e) 815 N Question 2 Jacques and George meet in the middle of a lake while paddling in their canoes. They come to a complete stop and talk for a while. When they are ready to leave, Jacques pushes George's canoe with a force to separate the two canoes. Which statement below is the most correct concerning the system of the two canoes, Jacques, and George? Please neglect any resistance due to the water? (a) The final momentum is in the direction of (b) The final momentum is in the direction opposite of but the final kinetic energy is zero. but the final kinetic energy is zero. (c) The final momentum is in the direction of and the final kinetic energy is positive. (d) The final momentum is zero and the final kinetic energy is zero. (e) The final momentum is zero but the final kinetic energy is positive. Question 3 A block of mass m is pushed against an ideal spring of spring constant k. The spring is compressed by a distance d, the block is then released. It is launched by the spring along a horizontal frictionless surface with a final speed v. A second block, this one having mass 4m is pushed against the same spring by distance 6d and released. What is the final speed of the block in this case? (a) v (b) 2v (c) 3v (d) 4v (e) 5v Page 2 of 6

3 The following three questions concern the same situation: A ball with no initial velocity falls vertically from an initial height of 2.1 m to the floor and bounces vertically, reaching a highest point of 1.7 m from the floor as illustrated. Take the zero of the potential energy of the ball to be at the floor. The mass of the ball is kg. Question 4 What is the loss of mechanical energy due to bouncing? (a) 13% of the initial potential energy (b) 19% of the initial potential energy (c) 24% of the initial potential energy (d) 28% of the initial potential energy (e) 31% of the initial potential energy Question 5 What is the magnitude of the impulse on the ball from the floor when the ball bounces? (a) 0.27 N s (b) 0.39 N s (c) 0.84 N s (d) 1.15 N s (e) 1.46 N s Question 6 Suppose instead that the mechanical energy is conserved during the bounce. Then the magnitude of the impulse on the ball from the floor would be (a) larger than the case with energy loss. (b) smaller than the case with energy loss. (c) the same as the case with energy loss (d) Insufficient information is provided to give a definite answer. Question 7 There is a merry-go-round of radius 3 m, which completes one rotation every 2.5 seconds at a constant angular velocity. You are standing on the edge of the merry-go-round. What is your acceleration? (a) 10 m/s 2 outward (b) 10 m/s 2 tangent to the edge (c) 10 m/s 2 inward (d) 20 m/s 2 outward (e) 20 m/s 2 inward Question 8 A kg crate sits on the back of a truck. The truck is accelerating to the right at 1.00 m/sec 2. The static coefficient of friction between the crate and the truck is μ s = The kinetic coefficient is μ k = The crate does not slide relative to the truck bed. The magnitude of the friction force on the crate is: (a) 490 N (b) 294 N (c) 200 N (d) 50 N (e) 30 N Page 3 of 6

4 FREE-FORM PART (16 points total) Clearly show your reasoning and work as some part marks may be awarded. Write your final answers in the boxes provided. PART A Block A is suspended vertically by an ideal string that passes over an ideal pulley and is then connected to Block B (1.6 kg) that is resting on an incline with = 35 as shown in the figure. There is friction between the incline and block B. The system is released from rest and block A is observed to accelerate downwards at a rate of 1.8 m/s 2. The tension in the string is measured to be 20 N. The questions below concern the system after it has been released. A1. [5 points] Calculate the mass of block A. m = A2. [5 points] Calculate a numerical value for the magnitude of the frictional force on box B due to the incline. f F = Page 4 of 6

5 PART B A puck of mass m 1 = 0.20 kg is sliding on an ice table without friction. Its initial velocity is along the x-axis with v 0 = 10.0 m/s as shown in the figure. The puck collides elastically with an identical puck, m 2, which is initially at rest. The pucks exit the collision as shown in the figure. It is observed that, after the collision, the velocity components of puck 2 are (v 2fx, v 2fy ) = (8.6 m/s, -3.4 m/s). (Ignore the effects of gravity, all the pieces are moving in a horizontal plane, and you may neglect friction). B1[3 points]. What the speed of puck 1 after the collision? B2[3 points]. What is angle in the diagram above? Page 5 of 6

6 ROUGH WORK (not marked) Page 6 of 6