29. What is the number of the half-lives required for a radioactive element to decay to about 6% of its original activity? (please choose the nearest number)
(A) 2
(B) 3
(C) 4
(D) 5
(E) 6

複選題25. Which one of the following molecules has a dipole moment but without polarity? (AB) O3 (AC) PH3 (AD) NH3 (AE) PCl5 (BC) H2O2 (BD)一律送分

26. Consider the following processes:Calculate ΔH for: C → E + 3D (A) 0 kJ/mol (B) 10 kJ/mol (C) -10 kJ/mol (D) -20 kJ/mol (E) 20 kJ/mol

27. CdS can be described as cubic closest packed anions with the cations in tetrahedral holes. What fraction of the tetrahedral holes is occupied by the cations? (A) 0.125 (B) 0.25 (C) 0.50 (D) 0.75 (E) 1.0

28. For the reaction 3A(g) + 2B(g) → 2C(g) + 2D(g), the following data was collected at constant temperature. Determine the correct rate law for this reaction.  (A) Rate = k[A][B] (B) Rate = k[A][B]2 (C) Rate = k[A]3 [B]2 (D)(E) Rate = k[A]2 [B]

30. Identify the element of Period 2 which has the following successive ionization energies, in kJ/mol.   (A) Li (B) B (C) O (D) Ne (E) None of these

31. Based on an order-of-magnitude estimate, what is the radius of the Earth in the unit of kilometer (km)? Hint: The meter was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole along a great circle. (A) 2 (B) 4 (C) 6 (D) 8 (E) 10

32. A part of the square that has sides of length L is removed from one corner. The center of mass of the remainder moves from C to C'. The displacement of the x coordinate of the center of mass (from C to C') is ______. (A) (2/3)L (B) (1/6)L (C) (1/8)L (D) (1/10)L (E) (1/12)L

複選題33. The string and the pulley are massless, and the coefficient of static and kinetic frictions are 0.2 and 0.1, respectively, for both table 1 (T1) and 2 (T2). If m1 = 2 kg, m2 = 3 kg, and m = 1.5 kg, find the acceleration of m. (Gravitational acceleration g = 10 m/s2 )  (AB) 7.7 m2 /s (AC) 8.7 m2 /s (AD) 9.7 m2 /s (AE) 10.7 m2 /s (BC) 11.7 m2 /s (BD)一律送分

34. Aluminum Rod #1 has a length L and a diameter d. Aluminum Rod #2 has a length 2L and a diameter 2d. If Rod #1 is under tension T and Rod #2 is under tension 2T, how do the changes in length of the two rods compare? (A) They are the same. (B) Rod #1 has double the change in length that Rod #2 has. (C) Rod #2 has double the change in length that Rod #1 has. (D) Rod #1 has quadruple the change in length that Rod #2 has. (E) Rod #2 has quadruple the change in length that Rod #1 has.

35. A toy car is running on a banked circular track of radius 10 m, as shown below. If the car weighs 5 kg and on wet ice, find the maximum velocity for the car to keep on the track without skid. (Gravitational acceleration g = 10 m/s2 , cos30° = 0.87, cos60° = 0.5)  (A) 5.4 m/s (B) 7.6 m/s (C) 9.4 m/s (D) 12.6 m/s (E) 15.7 m/s