 PhysicsBowl 2010 (Part 2) Printer Friendly Version 26. An electron moving in the plane of the page at an angle of 30º to the horizontal enters a region with a constant magnetic field directed horizontally in the plane of the page as shown. At the instant that the electron enters the magnetic field, which best describes the direction of the resulting magnetic force on the electron? 27. The circuit shown contains a battery (of emf = Vbat ) with an internal resistance r connected to a rheostat (variable resistor). When the resistance of the rheostat is increased, which of the following statements is true?

28. Which of the following could produce an enlarged but inverted image of a real object?

29. A ball initially at rest falls without air resistance from a height h above the ground. If the ball falls the first distance h/2 in a time t, how much time is required to fall the remaining distance of h/2?

30. Chromatic aberration from a lens is a consequence of 31. An object of mass M starts from rest at the bottom of a fixed incline of height H . A person decides to push the object up the incline in one of two ways with an applied force shown in the diagram. In each of the trials, the object reaches the top of the incline with speed . How would the work done by the person on the block compare for the two trials? Assume the same constant non-zero coefficient of kinetic friction between the incline and the object for both trials.

The next two questions share the same information Base your answers to questions 32 and 33 on the information and diagram below.

 A rubber ball of mass 2.0 kg falling straight downward hits the ground with a speed of 0.90 m/s and then rebounds straight upward with a speed of 0.60 m/s. The collision time of the ball with the ground is t 0.25 s. Treat g = 10 m/sec2 for this situation.

32. What is the magnitude of the average acceleration (in units of m/s2) of the ball while it is in contact with the ground?
33. What is the magnitude of the average force (in units of Newtons) exerted by the ground on the ball while they are in contact? 34. A 4.0 kg object in deep space moves at a constant velocity of 10 m/s along the +x axis. The object suddenly explodes into 2 equal mass pieces. Immediately after the explosion, one piece is now moving directly along the –y axis with a speed of 8.0 m/s. What was the size of the impulse (in proper MKS units) provided to this piece now moving along the –y axis from the explosion? 35. A point object with mass M = 2.0 kg is attached a distance R = 1.75 meters from the fixed center of a disk as shown in the figure. The disk starts rotating from rest with constant angular acceleration 5.00 rad/s2 about an axis perpendicular to the plane of the page through the disk’s center. After how much time (in seconds) is the tangential component of the point object’s acceleration equal in magnitude to the centripetal component of the point object’s acceleration?
36. In terms of the seven fundamental SI units in the MKS system, the unit for capacitance is written as which of the following?
37. A positively charged particle is moved in a straight line to the right from position x = -4.0 m to position x = -2.0 m by an external agent. The electric potential at these positions in space are V(x = -4m) is 4.0 volts and V(x = -2m) is 2.0 volts . Which statement is true about the work done by the external agent moving the charge between these positions and the electric field component parallel to the direction of motion that the moving charged particle experiences? Assume the particle is moved at constant speed.

38. Two objects both move and uniformly accelerate to the right. At time t = 0 , the objects are at the same initial position but Object 1 has initial speed twice that of Object 2 Object 1 has one-half the acceleration of Object 2. After some time T, the velocity of the two objects is the same. What is the ratio of the distance traveled in this time T by Object 2 to that traveled by Object 1? 39. A strong bar magnet is held very close to the opening of a solenoid as shown in the diagram. As the magnet is moved to the left toward the solenoid, a conventional current through the resistor shown is directed from A to B. What is the direction of the force on the bar magnet because of the induced current in the solenoid and which magnetic pole does the “??” in the diagram represent?  40. A uniform, solid cylinder with a mass M and radius R is pulled by a horizontal force F acting through the center as shown. The cylinder rolls to the right without slipping. What is the magnitude of the force of friction between the cylinder and the ground?
IMPORTANT:
All Division 01 students STOP HERE. Your last answer should be number 40. Numbers 41-50 should remain blank for Division 01 students.
All Division 02 students continue to Questions 41 – 50.

41. Two spheres are heated to the same temperature and allowed to radiate energy to identical surroundings. The spheres have the same emissivity, but one sphere has twice the diameter of the other. If the smaller sphere radiates energy at a rate P, at what rate will the larger sphere radiate energy?
42. A comet moves in an elliptical orbit around the sun. As the comet moves from aphelion (the point on the orbit farthest from the sun) to perihelion (the point on the orbit closest to the sun), which of the following results is true? 43. Two ions travel perpendicular to the same uniform magnetic field. The ions carry the same charge and have the same path radius in the magnetic field. Which of the following quantities must be the same for the two ions?
44. A radioactive sample of gas has a half-life of 100 seconds. If there are initially 10000 of these gas molecules in a closed container, approximately how many of the molecules remain after a time of 250 seconds elapses? 45. For the ideal RL circuit shown, the resistance is R = 10.0 ohms, the inductance is L = 5.0 H and the battery has voltage Some time after the switch S in the circuit is closed, the ammeter in the circuit reads 0.40 A. At what rate is energy being stored by the inductor at this instant (in Watts)?
46. For the following nuclear reaction, what is the unknown labeled by X?  47. An open cylindrical container with very large radius is at rest a distance H above the ground at the edge of a platform. A tiny hole develops at the bottom of the container and water from the container squirts out horizontally landing a distance H from the edge of the platform. For the water to land at this location, what is the depth of the water L in the container? The figure is not drawn to scale and air resistance is ignored.
48. Which of the following wavelengths (in nm) of electromagnetic radiation will produce photoelectrons of the least kinetic energy if the radiation is incident on a material with a work function of 4.80 eV? 49. A monatomic ideal gas is the working substance for an engine that undergoes the cyclic process (ABCDA) shown in the PV diagram. The processes are all isochoric or isobaric with pressures between Po and 2Po and volumes between Vo and (3/2)Vo. What is the efficiency of this engine?
50. An object of mass m is initially at rest. After this object is accelerated to a speed of 2.40 x 108 m/sec, it collides with and sticks to a second object of mass m at rest. Immediately after the collision, what is the common speed of the two masses?

IMPORTANT: All Division 02 students STOP HERE. Your last answer should be number 50. Related Documents