课程名称：普通物理学(一) 课程性质：必修 课程范围：课本第5~10章 开课教师：蔡尚岳 开课学院：理学院 开课系级：资科一 考试日期(年月日)：2011/11/11 考试时限(Mins)：180min 试题本文： Multiple-choice questions(40%) 1. If an object is in equilibrium, which of the following statements is "not" true? (a)The speed of the object remains constant. (b)The acceleration of the object is 0. (c)The net force acting on the object is 0. (d)The object may be moving or at rest. (e)There are at least two forces acting on the object. 2.As a raindrop falls through the atmosphere, its speed initially changes as it falls toward the Earth. Before the raindrop reaches its terminal speed, does the magnitude of its acceleration (a)increase, (b)decrease, (c)stay constant at 0, (d)stay constant at 9.8m/s^2, or (e)stay constant at some other value? 3.An ice cube has been given a push and slides without friction on a level table. According to the concept of energy diagram, which is "correct?" (a)It is in stabel equilibrium, (b)It is in unstable equilibrium, (c)It is in neutral equilibrium. (d)It is not in equilibrium. (e)It can't be determined. 4.As a simple pendulum swings back and forth, the forces acting on the suspended object are the gravitational force, the tension in the supporting cord, and air resistance. Which of these forces does no work on the pendulum at any time? (a)the gravitional force, (b)the tension in the supporting cord, (c) the air resistance, (d)none of them. (e)all of them. 5.From the question 4, which of these forces does negative work on the pendulum at all times during its motion? (a)the gravitational force, (b)the tension in the supporting cord, (c)air resistance, (d)none of them, (e)all of them. 6.Which of the following statements about an object-Earth system is "not" true? (a)It can have kinetic energy and not gravitational potential energy. (b)It can have gravitational potential energy and not kinetic energy (c)It can have both types of energy at the same moment. (d)It can have neither. (e)None of the above statement. 7.If two particles have equal momenta, are their kinetic energies equal? (a) yes, always (b)no,never (c)yes, as lohng as they move along parallel lines, (d) no, except when their speeds are the same (e)it can't be determined. 8.Consider an object on a rotating disc at a distance r from the center, held in place on the disk by static friction. Which of the follwing statements is "not" true concerning about the object? (a)If the angular speed is constant, the object is not accelerated. (b)If the angular speed is constant, the object must have constant tangential speed. (c)The object has a tangential acceleration only if the disk has an angular acceleration. (d)If the disk has an angular acceleration, the object has both centripetal acceleration and a tangential acceleration. (e)The object always has a centripetal acceleration except when the angular speed is 0. 9.A base ball bat of uniform density is cut at the location of its center of mass. Which piece has the larger mass? (a)the piece of the right, (b)the piece on the left, (c)both pieces have the same mass, (d)impossible to determine. 图: http://ppt.cc/@tvn 10.A ball rolls without slipping down incline A, starting from rest. At the same time, a box starts from rest and slides down incline B, which is identical to incline A except that it is frictionless. Which arrives at the bottom first? (a)The ball arrives first. (b)The box arrives first. (c)Both arrive at the same time. (d)It is impossible to determine. Calculation Problems(60%) 1.(8%)The systems shown in the figure are in equilibrium. If the spring scales are calibrated in newtons(N), what do they read? Ignore the masses of the pulleys and strings and assume the pulleys and the inclineare grictionless and g=9.8m/s^2 图: http://ppt.cc/kG_H 2.(12%)9.00kg object starting from rest falls through a viscous medium and experience a resistive force propositional to the velocity give by the equation: v = mg/b[1-exp(-bt/m)]. The object reaches one half of its terminal speed in 5.54s. (a)Determine the terminal speed. (b)At what time is the speed of the object three-fourths the terminal speed? (c)How far has the object traveled in f=the first 5.54s of motion? 3.(10%)A block of mass 0.5kg is pushed against a horizontal spring of negligible mass until the spring is compressed a distance x. The force constant of the spring is 450N/m. When it is released, the block travels along a frictionless, horizontal surface to point A, the bottom of a vertical circular track of radius R=1.0m, and continues to move up the track. The block's speed at the bottom of the track is 12.0m/s, and the block expericenes an average friction force of 7N while sliding up the top of the track. (a)what is x? (b)If the block were to reach the top of the track, what would be its speed at that point? (c)Does the block actually reach the top of the track, or does it fall off before reaching the top? 图: http://ppt.cc/A1FN 4.(8%)A uniform piece of sheet metal is shaped as shown in the figure. Compute the x and y coordinates of the center of mass of the piece. (Hint:you don't actually need to know the mass for each sheet) 图: http://ppt.cc/62TY 5.(12%)2 gliders are set in motion on a horizontal air track. A spring of force constant k is attached to the back end of the secondglider. As shown in the figure, the first glider, of mass m1, moves to the right with speed v1 and the second glider, of mass m2, moves more slowly to the right with speed v2. When m1 collides tith the spring attached to m2, the spring compresses by a distance xmax, and the gliders then move apart again. Assume there is no friction in the air track, in terms of v1,v2,m1,m2, and k, find (a)the speed v at maximum compression, (b)the maximum compression xmax, and (c)the velocity of each glider after m1 has lost contact with the spring. (Hint:consider conservation of energy and momenta during whole process.) 图: http://ppt.cc/Z4FD 6.(10%)A long uniform rod of length L and mass M is pivoted about a fritionless ,horizontal pin through one end. The rod is nudged from rest in vertical position as shown in figure. At the instant the rod is horizontal, find (a)its angular speed, (b)the magnitude of its angular acceleration, (c)the x and y components of the acceleration and (d)the components of the reaction force at the pivot. (Hint: You hsould calculate the moment of inertia, I, for the rod first.) 图: http://ppt.cc/Zp;B --

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