39. A wheel of radius ? and moment of inertia I is mounted on a frictionless horizontal axle as shown in the figure. A light cord wrapped around the wheel supports an object of mass m. What is the linear acceleration of the object? (Gravitational acceleration is g)

(A)
(B)
(C)
(D)
(E)

複選題35. A block of mass 2 kg on a table is pushed by a force of 20 N directed with an angle of 30o downward from the horizontal as shown in the figure. The kinetic frictional coefficient is 0.2. What is the work done by the frictional force after traveling 10 m long? (Gravitational acceleration g = 10 m/s2) (AB) 10 J (AC) 30 J (AD) 40 J (AE) 50 J (BC) 60 J (BD)一律送分

36. A bullet is hitting and getting stuck in a wood cube, which is sitting on a frictionless table. For this bullet-wood system, which item is not conserved before and after the collision event? (A) total kinetic energy (B) total linear momentum (C) total angular momentum (D) total mass (E) None of the above.

37. An estimated force-time curve for a baseball struck by a bat is shown in the figure. From this curve, determine the average force exerted on the ball. (A) 3 kN (B) 5 kN (C) 6 kN (D) 7 kN (E) 9 kN

38. A ball of mass m is released from a height of ?. What is its speed when it is at a height of y? (Gravitational acceleration is g) (A) (B) (C)(D) (E)

40. A block with a speaker bolted to it is connected to a spring having spring constant k = 20 N m as shown in figure. The total mass of the block and speaker is 5 kg, and the amplitude of this unit’s motion is 0.5 m. The speaker emits sound waves of frequency 440 Hz. Determine the highest frequency heard by the person to the right of the speaker. (Assume that the speed of sound is 343ms) (A) 481 Hz (B) 471 Hz (C) 461 Hz (D) 451 Hz (E) 441 Hz

41. A wire of length L, Young’s modulus ?, and cross-sectional area A is stretched elastically by an amount ∆L . It behaves as a spring by using the Hooke’s law. What is the work done in stretching the wire by an amount ∆L? (A)(B)(C)(D)(E)

42. A balloon filled with air is pulled into a tank of water at room temperature. As the balloon sinks, the air pressure inside the balloon ______. (A) increases (B) remains the same (C) decreases (D) increases then decreases (E) decreases then increases

43. Ethanol of density ?? flows smoothly through a horizontal pipe that tapers in cross-sectional area from A1 to A2 (A1 = 2A2) as shown in the figure. The pressure difference between the wide and narrow sections of pipe is ∆P. What is the volume flow rate of the ethanol? (A) (B) (C) (D) (E)

44. An ideal monoatomic gas of one mole is at pressure P, volume V, and temperature T. The gas is heated at constant volume to 2T. Then the gas is allowed to expand at constant temperature to 2V. Finally, the gas cools at constant pressure to T. What is the net entropy change for this ideal gas? (The ideal gas constant is R) (A) R ln 2 (B) −R ln 2 (C) 0 (D) R ln 4 (E) not calculatable by the above information

45. The figure shows a closed cycle for a gas. From c to b, 60 J is transferred from the gas as heat. From b to a, 100 J is transferred from the gas as heat, and the magnitude of the work done by the gas is 80 J. From a to c, 400 J is transferred to the gas as heat. What is the work done by the gas from a to c? (A) -240 J (B) 240 J (C) 320 J (D) -320J (E) -160 J