51. A 5.0 A current flows along a wire with The wire resides in a uniform magnetic field T. The magnetic force acting on the wire is described by What is the value of C+D+E?
(A) 1.3 N
(B) 6.3 N
(C) 1.8 N
(D) 4.3 N
(E) 0.35 N

47. There is a laminar flow in a tube. When both the radius and length of the tube are doubled, how many times of flow resistance is changed? (A) (B) (C) (D) (E)

48. A steam of water of densityρ, cross-sectional area A, and speed υ strikes a wall that is perpendicular to the direction of the stream, as shown in the figure below. The water then flows sideways across the wall. The force exerted by the stream on the wall is ______. (A) (B) (C) (D) (E)

49. Water is flowing at 4.0 m/s in a circular pipe. If the diameter of the pipe decreases to 1/2 its former value, what is the velocity of the water downstream? (A) 16 m/s (B) 4.0 m/s (C) 1.0 m/s (D) 8.0 m/s (E) 2.0 m/s

50. A 5.0 nC point charge is embedded at the center of a nonconducting sphere (radius = 2.0 cm) which has a charge of -8.0 nC distributed uniformly throughout its volume. What is the magnitude of the electric field at a point that is 1.0 cm from the center of the sphere? (where electric constant k=9.0×109 N·m 2 /C2 ) (A) 9.0 × 104 N/C (B) 1.8 × 105 N/C (C) 2.7 × 105 N/C (D) 3.6 × 105 N/C (E) 7.2× 105 N/C

52. The current in an inductor (L = 40 mH) is described by with I in ampers and t in seconds. What is the magnitude of the emf induced in the inductor at t = 3.0 s? (A) 2.0 V (B) 0.080 V (C) 50 V (D) 0 V (E) 4.0 V

53. A stiff wire bent into a semicircle of radius a = 2.0 cm is rotated at constant angular speed 40 rev/s in a uniform 20 mT magnetic field. What is the amplitude of the emf induced in the loop? (A) 3.16 × 10-2 V (B) 3.16 × 10-3 V (C) 3.16 × 10-1 V (D) 1.98 × 10-2 V (E) 1.98 × 10-3 V

54. Three long wires parallel to the x axis carry currents as shown. If I = 20 A, what is the magnitude of the magnetic field at the origin point O? ( magnetic constant μ0 = 4π × 10-7 T·m/A ) (A) 19 μT (B) 28 μT (C) 37 μT (D) 47 μT (E) 58 μT

55. The coil shown below has 2 turns, a cross-sectional area of 0.20 m2 , and a field (parallel to the axis of the coil) with a magnitude given by B = (4.0 + 3.0t 2 ) T, where t is in s. What is the potential difference, VA - VC, at t = 3.0 s? (A) -7.2 V (B) +7.2 V (C) -4.8 V (D) +4.8V (E) -12 V

56. A series RLC circuit is connected to an ac source The resistance, capacitive reactance and inductive reactance are 40 Ω, 80 Ω, and 50 Ω respectively. What is the current () in the circuit? (A) 3.0 A (B) 0.040 A (C) 1.7 A (D) 1.4 A (E) 2.4 A

57. The rest mass of an electron isWhat is the kinetic energy of an electron with the speed of 0.80c? (The constant c is the speed of light in vacuum.) (A) (B) (C) (D) (E)