[领域] 大一普物ꬠ (题目相关领域) [来源] 课本练习 (课本习题、考古题、参考书...) [题目] [瓶颈] (写写自己的想法，方便大家为你解答) Exercises 1. A 2.5-kg object falls vertically downward in a viscous medium at a constant speed of 2.5 m/s. How much work is done by the force the viscous medium exerts on the object as it falls 80 cm? A. +2.0 J B. +20 J C. –2.0 J D. –20 J E. +40 J 2. A 3.0-kg block is on a horizontal surface. The block is at rest when, at t = 0, a force (magnitude P = 12 N) acting parallel to the surface is applied to the block causing it to accelerate. The coefficient of kinetic friction between the block and the surface is 0.20. At what rate is the force P doing work on the block at t = 2.0 s? A. 54 W B. 49 W C. 44 W D. 59 W E. 24 W 3. A 20-kg block on a horizontal surface is attached to a light spring (force constant = 8.0 kN/m). The block is pulled 10 cm to the right from its equilibrium position and released from rest. When the block has moved 2.0 cm toward its equilibrium position, its kinetic energy is 13 J. How much work is done by the frictional force on the block as it moves the 2.0 cm? A. –2.5 J B. –1.4 J C. –3.0 J D. –1.9 J E. –14 J 4. A 10-kg block on a rough horizontal surface is attached to a light spring (force constant = 1.4 kN/m). The block is pulled 8.0 cm to the right from its equilibrium position and released from rest. The frictional force between the block and surface has a magnitude of 30 N. What is the kinetic energy of the block as it passes through its equilibrium position? A. 4.5 J B. 2.1 J C. 6.9 J D. 6.6 J E. 4.9 J 5. A single conservative force Fx = (6.0x – 12) N (x is in m) acts on a particle moving along the x axis. The potential energy associated with this force is assigned a value of +20 J at x = 0. What is the potential energy at x = 3.0 m? A. +11 J B. +29 J C. +9.0 J D. –9.0 J E. +20 J 6. A 0.80-kg object tied to the end of a 2.0-m string swings as a pendulum. At the lowest point of its swing, the object has a kinetic energy of 10 J. Determine the speed of the object at the instant when the string makes an angle of 50° with the vertical. A. 5.6 m/s B. 4.4 m/s C. 3.3 m/s D. 5.0 m/s E. 6.1 m/s 7. A spring (k = 600 N/m) is placed in a vertical position with its lower end supported by a horizontal surface. A 2.0-kg block that is initially 0.40 m above the upper end of the spring is dropped from rest onto the spring. What is the kinetic energy of the block at the instant it has fallen 0.50 m (compressing the spring 0.10 m)? A. 5.3 J B. 6.8 J C. 6.3 J D. 5.8 J E. 6.5 J 1 8. A 2.0-kg block sliding on a rough horizontal surface is attached to one end of a horizontal spring (k = 250 N/m) which has its other end fixed. The block passes through the equilibrium position with a speed of 2.6 m/s and first comes to rest at a displacement of 0.20 m from equilibrium. What is the coefficient of kinetic friction between the block and the horizontal surface? A. 0.32 B. 0.45 C. 0.58 D. 0.19 E. 0.26 9. A 2000-kg truck traveling at a speed of 6.0 m/s makes a 90° turn in a time of 4.0 s and emerges from this turn with a speed of 4.0 m/s. What is the magnitude of the average resultant force on the truck during this turn? A. 4.0 kN B. 5.0 kN C. 3.6 kN D. 6.4 kN E. 0.67 kN 10. A 3.0-kg ball with an initial velocity of (4i + 3j) m/s collides with a wall and rebounds with a velocity of (–4i + 3j) m/s. What is the impulse exerted on the ball by the wall? A. +24i N s B. –24i N s C. +18j N s D. –18j N s E. +8.0i N s 11. A 2.0-kg object moving 5.0 m/s collides with and sticks to an 8.0-kg object initially at rest. Determine the kinetic energy lost by the system as a result of this collision. A. 20 J B. 15 J C. 30 J D. 25 J E. 5.0 J 12. A 3.0-kg mass sliding on a frictionless surface has a velocity of 5.0 m/s east when it undergoes a one-dimensional inelastic collision with a 2.0-kg mass that has an initial velocity of 2.0 m/s west. After the collision the 3.0-kg mass has a velocity of 1.0 m/s east. How much kinetic energy does the two-mass system lose during the collision? A. 22 J B. 24 J C. 26 J D. 20 J E. 28 J --

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