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

2. Suppose a block is placed on a rough surface inclined relative to the horizontal and the coefficient of static friction between the block and the rough surface is μS. Let the incline angle be increased from θ = 0 until the block starts to move. What is the critical angle θc at which this slipping just occurs? (A) θc= arctan(μS )  (B)θc= arccos(μS )(C)θc=arcsin(μS ) (D)θc =π/2 (E) None of the above.

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.

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

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)