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Physics 103: Lecture 29 Review I

Physics 103: Lecture 29 Review I. Final Exam: Dec. 17 th , Thursday (2009) 12:25 – 2:25 PM . The 2 hour exam will have about 30-35 questions, The exam will cover chapters 1 - 14. Room assignments are posted http://tycho.physics.wisc.edu/courses/phys103/fall09/finrooms.html.

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Physics 103: Lecture 29 Review I

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  1. Physics 103: Lecture 29Review I Final Exam: Dec. 17th, Thursday (2009) 12:25 – 2:25 PM. The 2 hour exam will have about 30-35 questions, The exam will cover chapters 1 - 14. Room assignments are posted http://tycho.physics.wisc.edu/courses/phys103/fall09/finrooms.html Physics 103, Fall 2009, U. Wisconsin

  2. Problem Solving in Physics (Science!?) • Identify the physical significance of the situation • The concepts that are present and relevant. • Translate the situation described to physics equations • Perhaps, the situation is best clarified by a diagram (make one) • Analyze the details of the situation to determine which concepts are needed • Jot down the numbers (and unit) associated with those given • Identify what is asked and what can be easily obtained • Choose the appropriate relationship between the concepts. (equation) • Obtain the answer • Check - does the answer make sense? • Check - are the units consistent? • Techniques • Try to work out the problem as far as possible algebraically • You should not complete the arithmetic solution from the outset • You SHOULD try the problems out before looking at the choices provided to get maximum benefit. Physics 103, Fall 2009, U. Wisconsin

  3. Kinematics • Two stones are released from rest at a certain height, one after the other. (a) Will the difference in their speeds increase decrease stay the same? (b) Will their separation distance increase decrease stay the same? (c) Will the time interval between the instants at which they hit the ground be smaller than, equal to, or larger than the time interval between the instants of their release? Equal to Physics 103, Fall 2009, U. Wisconsin

  4. Preflight 3 An European sports car dealer claims that his product will accelerate at a constant rate from rest to a speed of 100 km/hr in 8s. What is the speed after first 5 s of acceleration? 17.4 m/s  53.2 m/s      44.4 m/s    34.7 m/s      28.7 m/s Physics 103, Fall 2009, U. Wisconsin

  5. Motion in Gravity A rock is thrown straight up from the Earth’s surface. Which one of the following statements concerning the net force acting on the rock at the top of its path is true?      It is equal to zero for an instant. It is equal to the force used to throw it up but in opposite direction It is equal to the weight of the rock Its direction changes from up to down Its magnitude is equal to the sum of the force used to throw it up and its weight  Physics 103, Fall 2009, U. Wisconsin

  6. Preflight 6 Two gliders of unequal mass mA<mB are placed on a frictionless air track. Glider A is pushed horizontally as shown so that the gliders accelerate together to the right. Let FhA represent the magnitude of the force of the hand on the glider A. Let FBA represent the magnitude of the force exerted by the glider A on the glider B. Which one of the following is true?      FhA < FBA FhA = FBA FhA > FBA Newton’s Second Law: Net external, FhA-FBA, is causing block A to accelerate to the right. FBA < FhA Physics 103, Fall 2009, U. Wisconsin

  7. Preflight 7 Two gliders of unequal mass mA<mB are placed on a frictionless air track. Glider A is pushed horizontally as shown so that the gliders accelerate together to the right. Let FhA represent the magnitude of the force of the hand on the glider A. Let FBA represent the magnitude of the force exerted by the glider A on the glider B. Which one of the following is true?      FBA < FAB FBA = FAB FBA > FAB Newton’s Third Law Physics 103, Fall 2009, U. Wisconsin

  8. Preflight 8 Two gliders of unequal mass mA<mB are placed on a frictionless air track. Glider A is pushed horizontally as shown so that the gliders accelerate together to the right. How does the net force on glider B (FB) compare to the magnitude of the net force on glider A (FA)?      FB < FA FB = FA FB > FA Physics 103, Fall 2009, U. Wisconsin

  9. Forces/Momentum • A monkey clings to a rope that passes over a pulley. The monkey’s weight is balanced by the mass m of a block hanging at the other end of the rope; both monkey and block are motionless. In order to get to the block, the monkey climbs a distance L (measured along the rope) up the rope. (a) Does the block move as a result of the monkey’s climbing? (b) If so, in which direction and by how much? Physics 103, Fall 2009, U. Wisconsin

  10. Preflight 10 Now suppose the box next to you on the floor of an elevator is annoying you, and you want to push it out of the way. Because of static friction, you need to push the box with a minimum force F before it will start to move. During which of the following situations is the force F required to move the box smallest?     When the elevator is accelerating upward. When the elevator is moving upward with constant speed. When the elevator is stationary. When the elevator is moving downward with constant speed. When the elevator is accelerating downward. Physics 103, Fall 2009, U. Wisconsin

  11. Force/Work A boy swings a mass m tied to a string in a horizontal circle about his head. • How much work is done by the tension in the string? • If he swung it in a vertical circle, how much work is done by the tension in the string? Physics 103, Fall 2009, U. Wisconsin

  12. Preflight 5 How much power is needed to lift a 75-kg student vertically upward at a constant speed of 0.33 m/s?     25 W      12.5 W      243 W      115 W     230 W Physics 103, Fall 2009, U. Wisconsin

  13. Power Estimate the maximum power consumed by an elevator motor if it can carry no more than 10 people vertically upward at a constant speed of 0.33 m/s. (Assume that an average adult weighs about 150 lbs and that the elevator itself weighs as much as its maximum load.)      about 500 W. about 1000 W. about 2000 W. about 4000 W. about 8000 W. Physics 103, Fall 2009, U. Wisconsin

  14. Collisions A moving object collides with an object initially at rest. • Is it possible for both objects to be at rest after the collision? • Can one of them be at rest after the collision? • Is it possible to have a collision in which all kinetic energy is lost? NO YES YES Physics 103, Fall 2009, U. Wisconsin

  15. Statics A sign of mass M is hung 1 m from the end of a 4 m long beam (mass m) as shown in the diagram. The beam is hinged at the wall. What is the tension in the guy wire? wire q = 30o 1 m SIGN Physics 103, Fall 2009, U. Wisconsin

  16. N T 300 F mg Mg Solution 3m 2m Chose axis of rotation at support because F & N are not known Physics 103, Fall 2009, U. Wisconsin

  17. Preflight 11 The picture below shows three different ways of using a wrench to loosen a stuck nut. Assume the applied force F is the same in each case. In which case is the torque on the nut the biggest?      Case 1 Case 2 Case 3 • = F d sinq Longest lever arm, d 90o angle Physics 103, Fall 2009, U. Wisconsin

  18. Preflight 12 The picture below shows three different ways of using a wrench to loosen a stuck nut. Assume the applied force F is the same in each case. In which case is the torque on the nut the smallest?      Case 1 Case 2 Case 3 • = F d sinq Short lever arm, d Reduced 45o angle Physics 103, Fall 2009, U. Wisconsin

  19. Preflight 13 FL FR dL dR mg The picture below shows two people lifting a heavy log. Which of the two people is supporting the greatest weight? The person on the left The person on the right Both are supporting the same weight R L • For static equilibrium • Net force is zero, FL+FR = mg • Net torque must be zero, dL FL = dR FR, considering an axis of rotation at midway point of the heavy log. • Person to left has shorter lever arm - therefore, FL > FR Physics 103, Fall 2009, U. Wisconsin

  20. Rotational Motion A boy is whirling a stone around his head by means of a string. The string makes one complete revolution every second, and the tension in the string is T. The boy then speeds up the stone, keeping the radius of the circle unchanged, so that the string makes two complete revolutions every second. What happens to the tension in the string?      The tension increases to four times its original value. The tension increases to two times its original value. The tension is unchanged. The tension reduces to one half its original value. The tension reduces to one fourth its original value. Physics 103, Fall 2009, U. Wisconsin

  21. Elasticity A mass of 100 tonnes (105 kg) is lifted on a steel rod two cm in diameter and 10 m in length. (Young’s modulus is 210 109 N/m2) (a) How long does the rod stretch? Physics 103, Fall 2009, U. Wisconsin

  22. Fluids A cube of cork exactly 10 cm on a side is weighed in the open air on a balance scale. If the density of cork is known to be 300 kg/m3, then the weight as measured by the scale is: a) 2.94 N b) 2940 N c) >2.94 N d) > 2940 N e) < 2.94 N f) < 2940 N Physics 103, Fall 2009, U. Wisconsin

  23. Gases What is the rms speed of a molecule of He (A=4) in a one liter sample at -100 oC ? R = 8.3 J/mole K Physics 103, Fall 2009, U. Wisconsin

  24. Heat Transfer A cylindrical pan contains 2 liters of water. Its circular bottom (diameter 20 cm) is 3 mm thick and made of iron. The water is all boiled away exactly 5 minutes after it begins to boil. (Assume the water is always in thermal equilibrium and that no heat is lost through the sides.) What was the temperature T of the burner? 1 cal = 4.186 J kFe = 80 J/s m oC LV (water) = 540 kcal/kg Physics 103, Fall 2009, U. Wisconsin

  25. Second Law A heat engine operates between a high temperature reservoir at 1000 oC and a low temperature reservoir at 200 oC. What is the minimum heat it must reject to the low temperature reservoir in order to do 3000 J of work? Physics 103, Fall 2009, U. Wisconsin

  26. Entropy Half a liter of water is frozen. (Lf = 334 kJ/kg) The freezing changes its entropy by - 610 J/K + 610 J/K -3340 J/K +3340 J/K -1.22 kJ/K +1.22 kJ/K Physics 103, Fall 2009, U. Wisconsin

  27. Entropy For the previous problem, what is the entropy change per minute? Physics 103, Fall 2009, U. Wisconsin

  28. Preflight 1 The decibel intensity level of a jackhammer is 130 dB. Decibel intensity level of two jackhammers operating side by side is:      65 dB 130 dB 133 dB     144 dB      260 dB Physics 103, Fall 2009, U. Wisconsin

  29. l/2 Wave Speed Two canoes are 10 m apart on a lake. Each bobs up and down with a period of 4 s. When one canoe is at its highest point, the other canoe is at its lowest point. Both canoes are always within a single cycle of the waves. Determine the speed of the waves.      40 m/s. 80 m/s. 14 m/s. 2.5 m/s 5 m/s.  Physics 103, Fall 2009, U. Wisconsin

  30. Preflight 2 A string on a piano is tuned to produce middle C (f=261.63 Hz) by carefully adjusting the tension in the string. For a fixed wavelength, what is the frequency when this tension is doubled?      130.08 Hz     185.00 Hz 370.00 Hz    446.63 Hz      523.26 Hz Physics 103, Fall 2009, U. Wisconsin

  31. Preflight 4 A rope of length L is clamped at both ends. Which one of the following is not a possible wavelength for the standing waves on this rope? 2L/3      2L      L      4L      L/2 Physics 103, Fall 2009, U. Wisconsin

  32. Physics 103, Fall 2009, U. Wisconsin

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