71A sprinter running the 100meter dash is known to accelerate for the * 1 point first few seconds of the race and then to run at constant speed the rest of the way. It is desired to design an experimental investigation to determine the sprinter's maximum speed v. Which of the following procedures could correctly make that determination? (A) Place poles 90 m and 100 In from the race's start. Measure with a stopwatch the time t for the sprinter to travel between the poles. To nd v, divide 10 mby I. (B) Estimate that the sprinter accelerates for the rst 2.5 5. Mark on the track the location of the sprinter after 2.5 5. Use a measuring tape to nd the distance d the sprinter traveled in this time. Divide d by 2.5 s to get v. (C) Measure with a stopwatch the time I for the sprinter to run the 100 m To nd v, divide 100 m by I. (D) Measure with a stopwatch the time t for the sprinter to run the 100 In. Divide I00 111 by t2 to get the average acceleration 0. Then since the sprinter starts from rest, v is given by "2(a)(100 111). Your answer (D This is a required question Figure below for question 8. d M1 M2 8. Two blocks of known masses M, and M2, with M, > M2, are connected by string over a freely rotating light pulley, as shown in the preceding diagram. A video camera records the motion of the blocks and pulley after the blocks are released from rest in the position shown. It is desired to use the video to measure the angular velocity of the pulley when block my has fallen a known distance d. Which of the following approaches will best make this experimental determination?Description of an experiment 1 point (A) Treat the system as a single nnss. The net force is the difference between the blocks' weights, mig ng; Newton's second law m1 - m: _ m. + rm _ equation yfz = 902 -|- Zadwith yo = 0 to deternnne the nal speed of the block; then the angular velocity is this speed divided by the radius of the pulley. (B) Mark a spot on the edge of the pulley. Run the video until the blocks have gone the distance d. In that time, count the total revolutions that spot nukes, including any partial revolutions measured using a protraetor. Divide the total revolutions by the time the video ran to get the angular velocity. (C) Pause the video when mass at; has just reached the distance (I; note the location of a position on the rim of the pulley. Advance the video one frame. Use a protractor to measure the angle through which the noted location on the pulley moved in that one 'ame. Divide that angle by the camera's time between frames to get the angular velocity of the pulley. (D) Make a graph of the position of mass ml as a mction of time, determining the block's position by pausing the video after every franc. The slope of this graph is the pulley's angular velocity. gives an acceleration of a = ] 3. Use the kinematic Your answer 9. 1 point -2 000800080800 N 2 080080080 9. Two hanging blocks, each attached to a different spring, undergo oscillatory motion. It is desired to determine, without stopping the motion, which block experiences the greater maximum acceleration. Which of the following procedures would accomplish that determination? (A) Place a motion detector underneath each block. On the velocity-time graphs output by the detector, look at the maximum vertical axis value, indicating the highest speed that block attained. Whichever block attains the higher speed has the larger acceleration. (B) Place a motion detector underneath each block. On the velocity-time graphs output by the detector, look at the steepest portion of the graph. Whichever block makes the steeper maximum slope on the velocity-time graph has the greater maximum acceleration. (C) Place a motion detector underneath each block. On the position-time graphs output by the detector, look at the maximum vertical axis value, indicating the amplitude of the motion. Whichever block oscillates with the larger amplitude has the larger acceleration. (D) Place a motion detector underneath each block. On the position-time graphs output by the detector, look at the steepest portion of the graph. Whichever block makes the steeper maximum slope on the position-time graph has the greater maximum acceleration. Your answer10. * 1 point 10. In the laboratory, measured net torques t are applied to an initially stationary pivoted bar. The resulting change in the bar's angular speed after 1 s is measured and recorded as An. Which of the following graphs will produce a slope equal to the bar's rotational inertia about the pivot point? (A) T versus Aw (B) T versus Aw (C) r versus (Aw)2 (D) + versus VAw Your answer11. * 1 point Rest 2 m/s 1 kg 0.5 kg Questions 11 and 12: A 1-kg cart moves to the right at 2 m/s. This cart collides with a 0.5-kg cart that is initially at rest; the carts stick together after the collision. Friction on the surface is negligible. 11. What is the kinetic energy of the two-cart system after the collision? (A) 1.3 J (B)OJ (C) 0.7 J (D) 2 J Your answer12. * 1 point 12. If instead the carts collide elastically, which of the following is correct about the linear momentum and kinetic energy of the two-cart system after the collision compared to the collision in which the carts stuck together? (A) The linear momentum and the kinetic energy will both be greater. (B) The linear momentum will be greater, but the kinetic energy will be the same. (C) The kinetic energy will be greater, but the linear momentum will be the same. (D) The linear momentum and the kinetic energy will both be the same. Your answerMultiple correct * 1 point 13. (multiple correct) An astrophysicist is modeling the behavior of stars orbiting the center of the Milky Way galaxy. In his model, he must consider the effect of each of the four fundamental natural forces. Which of the following correctly indicates a negligible force with a correct explanation for neglecting that force? Select two answers. (A) The gravitational force is negligible, because the order of magnitude of the gravitational constant G (10- N.m?/kg?) is extraordinarily small compared to the order of magnitude of the Coulomb's law constant (k = 109 N.m-/C2). (B) The electric force is negligible, because it cannot act beyond atomic (~10-10 m) distances. (C) The weak force is negligible because although it is responsible for a star's energy release via nuclear fusion, the nuclear nature of the weak force means that it is irrelevant for star-to-star interactions at a distance. (D) The strong force is negligible because it cannot act beyond nuclear (~10-15 m) distances. Your answerMultiple correct * 1 point 14. (multiple correct) A car tire initially rotates clockwise with a rotational speed of 20 rad/s. The rotation gradually slows, such that 2 s later the tire rotates clockwise with a rotational speed of 10 rad/s. Considering clockwise as the positive direction, which of the following vectors is positive? Select two answers. (A) the tire's angular acceleration (B) the tire's angular momentum (C) the net torque on the tire (D) the tire's angular velocity Your answerMultiple correct * 1 point Path of electron's motion e 15. (multiple correct) An electron in a vacuum chamber is moving at constant velocity in the direction shown in the preceding diagram. Which of the following force vectors F applied to the electron would increase the electron's kinetic energy? Select two answers. (A) (B) F F (C) F (D) Your answer1. 1. (12 points) Motion detector A 500 kg B In Experiment 1, two carts collide on a negligible-friction track: Cart A with mass 500 g, and Cart B with unknown mass. Before the collision, Cart B is at rest Adhesive is attached to the carts such that after the collision, the carts stick together. The speeds of Cart A before collision and after collision are measured using the sonic motion detector, as shown in the diagram. (a) In one trial, the motion detector is turned on, Cart A is given a shove, the carts collide, and then the detector is turned off. The detector produces the velocity-time graph shown as follows. On the graph, indicate with a circle the portion of the graph that represents the collision occurring. Explain how you figured this out.b. 0.6 0.4 Velocity (m/s) 0.2 0.0 2 Time (s) (i) Use the graph to estimate the speed of Cart A before the collision. (ii) Use the graph to estimate the speed of Cart A after the collision. (b) In numerous trials, the speeds of Cart A before and after the collision are measured. You are asked to construct a graph of this data whose slope can be used to calculate the mass of Cart B. (i) What should you graph on each axis? (ii) Explain in several sentences how you will use the slope of this graph to calculate the mass of Cart B. Be specific both about the calculations you will perform, and about why those calculations will produce the mass of Cart B.C. (c) In Experiment 2, the adhesive is removed such that the carts bounce off of one another. The motion detector is again positioned to read the speed of Cart A before and after collision. (i) Describe an experimental procedure by which the speed of Cart B after collision can be measured. You may use any equipment available in your physics laboratory, but you may not use a second sonic motion detector. (ii) The masses of Carts A and B are now both known; the speeds of both carts before and after collision have been measured. Explain how you could determine whether the collision in Experiment 2 was elastic. Be sure to describe specifically the calculations you would perform, as well as how you would use the results of those calculations to make the determination