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General Physics – ph 211 Name:____________ Midterm II (Ch 5 – 7) Type A February 22, 2005 Exam is closed book and closed notes. Use only your note card. Write all work and answers in the papers provided. Show all your work and explain your reasoning (No credit will be given for an answer that does not include the necessary solution or explanation, except for true/false or multiple choice questions) Partial credit may be awarded for a correct method of solution, even if the answer is wrong. Part I – True or False (4 points each): For questions 1 – 5, state whether each statement is true or false. 1. The motion of an object is always in the direction of the resultant force acting on it. 2. The force of static friction always equals sFN. 3. The force of kinetic friction always equals kFN. 4. An object can not move in a circle unless there is net force acting on it. 5. Work is the area under the force-versus-time curve. 6. Work is the area under the force-versus-position curve. 7. Power is a vector quantity. 8. Power is a scalar quantity. 9. When a ball is thrown upward, it reaches its maximum height when the force pushing it up is equal to its weight. 10. The acceleration of an object does not have to be in the same direction as the net force applied to it. Part II – Multiple Choice (4 points each): Choose the one correct answer for each of the following questions that best answers or completes the question. 11. If the net force on a moving object is suddenly reduced to zero, as a consequent the object A) stops over a short distance. B) stops abruptly. C) changes direction. D) changes velocity in an unknown way. E) continues its motion at constant velocity 12. A block whose weight is 20 N rests on a horizontal surface. The coefficient of static friction between the block and supporting surface is 1.0. The block is pushed by a force of 20 N that makes an angle of 30o with the horizontal as shown in the diagram. T = 20 N 300 A) The block will remain at rest, and fs = 17.3N 20 N s=1.0 B) The block will move horizontally. C) The block will be lifted off the surface by the string. D) The block will remain at rest; the force of static friction is less than 17.3 N. Ph 211 midterm 1, W2005 1 13. A block whose weight is 20 N rests on a horizontal surface. The coefficient of static friction between the block and supporting surface is 1.0. A string is attached to the block. The tension in the string is 20 N, and the string makes an angle of 30o with the horizontal. T = 20 N 300 A) The block will remain at rest, and fs = 17.3N 20 N s=1.0 B) The block will move horizontally C) The block will be lifted off the surface by the string. D) The block will remain at rest; the force of static friction is less than 17.3 N. 14. The work done to accelerate a car from 0 to 30 m/s A) is more than the work required to accelerate it from 30 m/s to 60 m/s. B) is equal to the work required to accelerate it from 30 m/s to 60 m/s. C) is less than the work required to accelerate it from 30 m/s to 60 m/s. D) may be any of the above depending on the rate at which the work is done. 15. A ball is tied to the end of a string and swung in a vertical circle on earth. The tension in the string is constant. Speed of the ball is A) larger at the top. C) the same at top and bottom. B) larger at the bottom. 16. A ball is tied to the end of a string and swung in a vertical circle on earth. The speed of the ball is kept constant. The tension in the string is A) larger at the top. C) the same at top and bottom. B) larger at the bottom. 17. What is (are) the SI units of force divided by acceleration. A) kg B) m/s C) kg m/s2 D) m/s2 E) J 18. What is (are) the SI units of force divided by mass. A) kg B) m/s C) kg m/s2 D) m/s2 E) J Part III – Problems (20 points each): Show your work clearly and completely for each of the following problems. A 4.5kg block is moving with speed of 11 m/s up an inclined plane that makes an angle of 30o with the horizontal. The block slides a distance of 2.4 m in 5.2 s before it comes to rest. A) Draw the free body diagram showing all forces acting on the block. What is the acceleration of the block? C) Calculate the magnitude of the normal force on the block. D) Calculate the coefficient of kinetic friction between the block and plane. Ph 211 midterm 1, W2005 2 20. A 5.1-kg metal ball is suspended from the ceiling by a 1.4 m thread of negligible mass. The ball is pulled to an angle of 27o from vertical position and set in motion in a horizontal circle so that the thread describes a cone. The angle the thread is A) Draw the free body diagram showing all forces acting on the ball. B) What is the tension in the string when the ball is in circular motion? C) What is the speed of the ball when it is in circular motion? 21. A box of mass 4.0 kg is pushed up a frictionless incline plane by a worker who applies a horizontal force of 150 N. The incline is at angle of above horizontal, where sin0.60 and cos= 0.80. The box moves 3.0 m along the incline. Assume g = 10 m/s2. A) How much work is done on the box by the worker? B) How much work is done on the box by gravity? C) How much work is done on the box by the normal force of the incline? D) What is the final speed of the box, assuming it started at rest. Ph 211 midterm 1, W2005 3