38. It takes time T for M gram(s) of a radioactive substance to decay to M /4 gram(s). How long does it take for M/4 gram(s) of the substance to decay to M /8 gram(s)?
(A)2T
(B)T
(C)T/2
(D)T²
(E)

34. A block of density 800 kg/m3 floats face down in a fluid of density 1200 kg/m3. The block has height H= 6 cm. If the block is held fully submerged and then released, what is the magnitude of its initial acceleration? (A) 2.45 m/s2 (B)19.6 m/s2(C)0m/s2 (D)9.8 m/s2 (E) 4.9 m/s2

35. What is the pressure difference between the heart and the brain of a man if the brain is 40 cm above the heart? (The density of blood is 1.05 g/cm3) (A)411.6Pa(B)4116Pa(C)41160Pa(D)411600Pa(E)41.16 Pa

36. A Mashlight uses two 1.5-V batteries. If the current passing through the lightbulb is 0.5 A. how much energy is consumed by the lightbulb in half an hour? (A)45J (B)90J (C)900J (D) 2700 J (E) 10800 J

37. A circuit, as shown in the right figure, contains four inductors of L1=20.0 mH, L2=30.0 mH, L3 =40.0 mH, and L4 =50.0 mH. What is the equivalent inductance of the cireuit?(A) 102 mH (B) 15.38 mH (C) 140mH (D) 7.81 mH (E) 60 mH

39. A 5.0-kg ball is dropped from a cliff. Given the resistive force is R = (0.49 kg/m)v2, where v is the speed of the ball, and the gravitational acceleration is g = 9.8 m/s2, what is the terminal speed the ball? (A) 4.9 m/s (B) 10 m/s (C)40 m/s (D) 2.0 m/s (E) 20 m/s

40. In the figure, the string is tensioned by a hanging block of mass m and can vibrate with a fundamental frequency f. If one wants to create a fundamental frequency of 2f, what should the block's mass be?(A)m (B) (C)2m (D)m/2 (E)4m

41. The force  in the figure will keep the block and the pulleys in equilibrium. The block has mass m. Neglect the mass of pulleys and strings and friction in the system. What is the strength of?(A)mg (B)mg/3 (C)mg/5 (D)mg/7 (E) mg/9

42. At one instant, a force acts on a 0.25 kg object that has position vectorand velocity What is the object's angular momentum about the origin? (A) -1.5 kg m2/s (B) 1.5 kg m2/s (C) -0.75 kg m2/s(D) -0.375 kg m2/s(E)0 kg m2/s

43. A jet aircraft of speed 200 m/s is making a vertical circular loop of radius 2 km. What is the force exerted by the seat on the 60-kg pilot at the top of the loop? (Gravitational acceleration g = 9.8 m/s2) (A)12N(B)24 N (C)306N (D) 612 N (E) 48 N

44. Four objects are released from rest at the top of an inclined plane and roll down the plane (see the figure). A is a solid sphere. B is a hollow sphere, C is a solid cylinder, and D is a hollow cylinder. All of the four objects have identical radii and masses. Assume that the objects roll without slipping. Which one would win the race?(A) A (B) B (C) C (D) D (E) AIl arrive at the end of the inclined plane at the same time.