Los Altos Physics Spring 2006 MC Sample Multiple Choice Questions Choose the best answer and write the corresponding letter in the space provided on the solution workbook. Version # 1_ 1. A football player kicks a 0.41-kg football initially at rest; and the ball flies through the air. If the kicker's foot was in contact with the ball for 0.051 s and the ball's initial speed after the collision is 21 m/s, what was the magnitude of the average force on the football? A) 46 N B) 170 N C) 210 N D) 81 N E) 9.7 N The figures show standing waves of sound in six organ pipes of the same length. Each pipe has one end open and the other end closed. Note: some of the figures show situations that are not possible. 2. Which one of the pipes is resonating in its third harmonic? A) 1 B) 2 C) 3 D) 4 E) 6 Page 1
The diagram shows the various positions of a child in motion on a swing. Somewhere in front of the child a stationary whistle is blowing. 3. At which position(s) will the child hear the highest frequency for the sound from the whistle? A) at both A and D B) at B when moving toward A C) at B when moving toward C D) at C when moving toward B E) at C when moving toward D Three resistors are connected as shown in the figure. The potential difference between points A and B is 26 V. 4. What is the equivalent resistance between the points A and B? A) 5.1 O B) 9.0 O C) 6.8 O D) 4.3 O E) 3.8 O Page 2
5. How much current flows through the 3-O resistor? A) 4.0 A B) 10.0 A C) 2.0 A D) 6.0 A E) 8.7 A 6. Two particles move through a uniform magnetic field that is directed out of the plane of the page. The figure shows the paths taken by the two particles as they move through the field. The particles are not subject to any other forces or fields. Which one of the following statements concerning these particles is true? A) Particle 1 is positively charged; 2 is negative. B) Particle 1 is negatively charged; 2 is negative. C) The particles may both be neutral. D) Particle 1 is negatively charged; 2 is positive. E) Particle 1 is positively charged; 2 is positive. 7. A rock is dropped from a high tower and falls freely under the influence of gravity. Which one of the following statements is true concerning the rock as it falls? A) The amount of momentum it gains will be proportional to the amount of potential energy that it loses. B) It will gain an equal amount of speed for each meter through which it falls. C) It will gain an equal amount of momentum for each meter through which it falls. D) It will gain an equal amount of momentum during each second. E) It will gain an equal amount of kinetic energy during each second. 8. A certain string, clamped at both ends, vibrates in seven segments at a frequency of 2.40 10 2 Hz. What frequency will cause it to vibrate in four segments? A) 137 Hz B) 420 Hz C) 89 Hz D) 274 Hz E) 411 Hz Page 3
The figure shows a uniform, 3.0-T magnetic field that is normal to the plane of a conducting, circular loop with a resistance of 1.5 O and a radius of 0.024 m. The magnetic field is directed out of the paper as shown. Note: The area of the non-circular portion of the wire is considered negligible compared to that of the circular loop. 9. What is the magnitude of the average induced emf in the loop if the magnitude of the magnetic field is doubled in 0.4 s? A) 0.027 V B) 0.014 V C) 0.038 V D) 0.65 V E) 0.43 V 10. Two cars of equal mass collide on a horizontal frictionless surface. Before the collision, car A is at rest while car B has a constant velocity of 12 m/s. After the collision, the two bodies are stuck together. What is the speed of the composite body (A + B) after the collision? A) 36 m/s B) 3.0 m/s C) 6.0 m/s D) 12 m/s E) 24 m/s Page 4
A 2.0-kg object moves in a straight line on a horizontal frictionless surface. The graph shows the velocity of the object as a function of time. The various equal time intervals are labeled using Roman numerals: I, II, III, IV, and V. The net force on the object always acts along the line of motion of the object. 11. Which section(s) of the graph correspond to a condition of zero net force? A) I, III, and V B) II, III, and IV C) V only D) II and IV E) III only 12. Which section of the graph corresponds to the application of the largest constant net force? A) I B) II C) III D) IV E) V 13. In which section(s) of the graph is the net force changing? A) II and IV B) I and V C) IV D) I and III E) III Page 5
14. A force of magnitude 25 N directed at an angle of 37 above the horizontal moves a 10- kg crate along a horizontal surface at constant velocity. How much work is done by this force in moving the crate a distance of 15 m? A) 1.7 J B) 40 J C) 300 J D) zero joules E) 98 J 15. A grindstone, initially at rest, is given a constant angular acceleration so that it makes 20.0 rev in the first 8.00 s. What is its angular acceleration? A) 1.97 rad/s 2 B) 3.93 rad/s 2 C) 0.625 rad/s 2 D) 2.50 rad/s 2 E) 0.313 rad/s 2 A projectile is fired from a gun and has initial horizontal and vertical components of velocity equal to 30 m/s and 40 m/s, respectively. 16. Approximately how long does it take the projectile to reach the highest point in its trajectory? A) 2 s B) 4 s C) 8 s D) 16 s E) 1 s 17. What is the speed of the projectile when it is at the highest point in its trajectory? A) 30 m/s B) 0 m/s C) 50 m/s D) 20 m/s E) 40 m/s Page 6
18. What is the acceleration of the projectile when it reaches its maximum height? A) Its magnitude is 9.8 m/s 2 ; and its direction is changing. B) zero m/s 2 C) less than 9.8 m/s 2 and non-zero. D) 9.8 m/s 2, downward E) 4.9 m/s 2, downward A 1000-kg car travels along a straight 500-m portion of highway (from A to B) at a constant speed of 10 m/s. At B, the car encounters an unbanked curve of radius 50 m. The car follows the road from B to C traveling at a constant speed of 10 m/s while the direction of the car changes from east to south. 19. What is the magnitude of the frictional force between the tires and the road as the car negotiates the curve from B to C? A) 5000 N B) 1000 N C) 2000 N D) 10 000 N E) 20 000 N 20. What is the magnitude of the acceleration of the car as it travels from B to C? A) 20 m/s 2 B) 10 m/s 2 C) zero m/s 2 D) 5 m/s 2 E) 2 m/s 2 Page 7
An 80-kg man balances the boy on a teeter-totter as shown. Note: Ignore the weight of the board. 21. What is the approximate mass of the boy? A) 50 kg B) 10 kg C) 20 kg D) 40 kg E) 45 kg 22. An electron enters a region that contains a magnetic field directed into the page as shown. The velocity vector of the electron makes an angle of 30 with the +y axis. What is the direction of the magnetic force on the electron when it enters the field? A) at an angle of 30 above the positive x axis B) up, out of the page C) at an angle of 60 below the positive x axis D) at an angle of 60 above the positive x axis E) at an angle of 30 below the positive x axis 23. The kinetic energy of a car is 8 10 6 J as it travels along a horizontal road. How much work is required to stop the car in 10 s? A) 8 10 5 J B) 8 10 7 J C) 8 10 6 J D) 8 10 4 J E) zero joules Page 8
The figure shows an equilateral triangle ABC. A positive point charge +q is located at each of the three vertices A, B, and C. Each side of the triangle is of length a. A point charge Q (that may be positive or negative) is placed at the mid-point between B and C. 24. Is it possible to choose the value of Q (that is non-zero) such that the force on Q is zero? Explain why or why not. A) Yes, because the forces on Q are vectors and three vectors can add to zero. B) No, because the forces on Q are vectors and three vectors can never add to zero. C) Yes, because the electric force at the mid-point between B and C is zero whether a charge is placed there or not. D) No, because the forces on Q due to the charges at B and C point in the same direction. E) No, because a fourth charge would be needed to cancel the force on Q due to the charge at A. 25. Determine an expression for the magnitude and sign of Q so that the net force on the charge at A is zero newtons. A) Q 4 3 = q 3 B) Q 4 3 =+ q 3 C) Q 3 3 = q 4 D) Q 3 3 =+ q 4 E) 3 Q =+ q 4 3 Page 9
Physics Spring 2006 Multiple Choice Sample Answer Key 1. B 2. D 3. E 4. D 5. D 6. B 7. D 8. A 9. B 10. C 11. D 12. C 13. B 14. C 15. B 16. B 17. A 18. D 19. C 20. E 21. C 22. E 23. C 24. E 25. C Page 10