7. The position of a particle is given by the expression x= 4 cos( 3 πt + π), where x is in meters and t is in seconds. What is the frequency?
(A) 1.0 Hz
(B) 1.5 Hz
(C) 3.0 Hz
(D) 4.0 Hz
(E) 9.4 Hz

3. An escalator is used to move 20 people (60 kg each) per minute from the first floor of a department store to the second floor, 5 m above. The power required is approximately ______. (A) 100 W (B) 200 W (C) 1000 W (D) 2000 W (E) 4000 W

4. An air-bag company is designing a new product. The specification requires passengers of mass 75 kg to sit in a car traveling at 60 km/h. When the car hits the wall and stops there, the air-bag extends the stopping time up to 0.4 s. What is the average force on the passenger during this collision? (A) 408 N (B) 1680 N (C) 3125 N (D) 11259 N (E) 30625 N

5. The electric inductance L is defined as the magnetic flux ΦB divided by current I. What is the unit of the inductance L divided by electric resistance R ? (A) tesla (B) Hz (C) Wb (D) sec (E) None of the above.

6. A hydraulic press has one piston of diameter 2 cm and the other piston of diameter 8 cm. What force must be applied to the smaller piston to obtain a force of 1600 N at the larger piston? (A) 6 N (B) 25 N (C) 100 N (D) 400 N (E) 1600 N

8. The average molecular translational kinetic energy of a gas molecule is ______. (The ideal gas constant is R. Boltzmann constant is kB. Temperature of gas is T.) (A) (3/2)kBT (B) (3/2)RT (C) (1/2)kBT (D) (1/2)RT (E) (n+3)kBT/2, where n is the number of internal degrees of freedom.

9. A gas in a cylinder starts from initial state i to finial state f through 4 different paths as shown in the figure. Regarding to the heat energy, work, and internal energy, which statements is incorrect?(A) Path 1 is isobaric expansion, gas must be heated. (B) Path 2 is isothermal expansion； no work is involved in this process. (C) Path 3 is adiabatic expansion, therefore no heat transfer occurred. (D) Path 4 is isochoric cooling； heat is extracted out of gas. (E) Gas do not do work for path 4 only.

10. A resistor of unknown resistance and a 15 Ω resistor are connected across a 20 V emf in such a way that a 2 A current is observed. What is the value of the unknown resistance? (A) 5 Ω (B) 7.5 Ω (C) 12 Ω (D) 30 Ω (E) 75 Ω

11. A conducting sphere of radius R contains a positive charge. Which figure correctly represents the magnitude of the electric field E as a function of the distance r from the center of the sphere? (A) (B)(C)(D)(E)

12. Which equation is not one of Maxwell’s equations? (A) (B) (C) (D) (E)

13. The flux of the electric fieldN/C through a 2 m2 portion of the xz plane is ______. (A) 16 N●m2 /C (B) −48 N●m2 /C (C) 48 N●m2 /C (D) −60 N●m2 /C (E) 60 N●m2 /C