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

31. The velocities of drivers A and B are shown as functions of time in the figure below. Driver B starts her car at the instant driver A passes her. At which moment on the graph are drivers A and B side by side? (A) 0 s, 2 s (B) 0 s, 4 s (C) 2 s, 4 s (D) 2 s, 6 s (E) 4 s, 6 s

32. A uniform cord has the mass per unit length λ and it is arranged as that shown in the figure. Here the tension is maintained by suspending an object of mass M from one end. What is the speed of a pulse on the cord if the tension force is not affected by the mass of the cord? (Gravitational acceleration is g) (A) (B) (C) (D) (E)

33. As shown in figures (a) and (b), a constant force F is applied to the two contact blocks in both cases. In figure (a), block A pushes against block B with a 20 N force directed horizontally to the right. In figure (b), block A pushes against block B with a 10 N force directed horizontally to the left. The total mass of two blocks is 12 kg. Which of the following statement is correct? (Gravitational acceleration g = 10 m/s2 )  (A) The magnitude of F is 20 N. (B) The mass ratio between block A and B is 2. (C) The acceleration in (a) is 1.5 m/s2. (D) The acceleration in (b) is 2.5 m/s2. (E) The mass of block A is 8 kg.

34. A force of acts on a particle, changing only the kinetic energy of the particle. How much work is done on the particle as it moves from (2, 3) to (3, 0)? (A) 6 (B) 5 (C) 3 (D) 2 (E) 1

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)

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)

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)