43. One quarter of a circular loop of wire carries a current I. The current I enters and leaves on straight segments of wire. The straight wires are along tiie radial direction ftom the center of the circular portion, Find the magnetic field at the center of tiie circular.
(A)
(B)
(C)
(D)
(E)

39. Calculate the recoil velocity of a 5-kg rifle that shoots a 0.02-kg bullet at a speed of 620 (m/s). (A)-10 m/s (B) -5 m/s (C) -2.5 m/s (D) -1,25 m/s (E) -1 m/s

40. Neglect the friction and weights of pulleys and cord in the figure. The body of mass m2 is falling down with acceleration a2 = g/2. What is the mass ratio m2/m1? (A)1 (B)3/2 (C)2 (D)5/2 (E)4

41. A block of mass m was placed on a surface (coefficient of kinetic friction μ) with an inclined angle θ. The block is initially moving uphill with speed v. What is the total distance dtiie block moves before the block goes downhill or stops?  (A)(B)(C)(D) (E)

42. A uniform stick 1.0 m long with total mass 15 kg rests on a firictionless table and is pivoted at its end. The uniform stick rotates freely about this pivot. A bullet with a mass of 10 g and a speed of400 m/s strikes the center of the stick, in a direction perpendicular to tiie stick and embeds itself there. Find the stick' s angular speed. (A) 0.1 rad/s (B) 0.4 rad/s (C) 0.6 rad/s (D) 02 rad/s (E) 0.8 rad/s 

44. A capacitor C is fully charged by a de power supply so that one plate has charge Q0. It is disconnected from the power supply and is connected to a inductor L, which results in an electrical oscillation. What is the angular frequency ω of the oscillation and its maximum current I0? (A)(B)(C)(D)(E)

45. What is the average translational kinetic energy of molecules in an ideal gas at 37°C? (A) 1.3x10-21 j (B) 2.6x10-21 j (C)4.2X10-21J (D) 5.2x10-21j (E) 6.4x10-21 J

46. In human, blood flows from the heart into the aorta, from which it passes into the major arteries. These branch into the small arteries (arterioles), which in turn branch into myriads of tiny capillaries. The radius of the aorta is about 1.2 cm, and the blood passing through it has a speed of about 40 cm/s. A typical capillary has a radius of about 4✖10-4 cm, and blood flows through it at a speed of about 5x10-4 m/s. Estimate the number of capillaries that are in the body. (A) 1✖109 (B) 3✖109 (C) 5✖l09 (D) 7✖109 (E)9✖109

47. An electron travels at 2✖107 m/s in a plane perpendicular to a uniform 0.01 T magnetic field. What is the radius of the travel path? (electron mass = 9.1✖10-31 kg, charge on electron = 1.6✖10-19 Coul) (A) 5.2 cm (B) 3.8 cm (C) 2.1 cm (D) 1.1 cm (E) 0.5 cm

48. A soap bubble appears green (wavelength:540 nm) at the point on its front surface nearest the viewer. What is the smallest thickness the soap bubble film could have? Assume that the index of refraction of the soap film is n=1.35. (A) 100 nm (B) 150 nm (C) 200 nm (D) 250 nm (E) 300 nm

49. An engine's heat input per second is 8.0 kJ at 500 K reservoir and output per second is 4.0kJ at 300 K reservoir. What is the Carnot efficiency of this engine? (A) 20% (B) 40% (C) 50% (D) 80% (E) none of the above