UNIVERSITY OF KWAZULU-NATAL SECOND SEMESTER EXAMINATION: 22 nd November 2010 Subject, Course and Code: Foundation Physics PHYS099 PY and PHYS199 PY

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1 UNIVERSITY OF KWAZULU-NATAL SECOND SEMESTER EXAMINATION: 22 nd November 2010 Subject, Course and Code: PHYS099 PY and PHYS199 PY DURATION: 3 HOURS TOTAL MARKS:180 INTERNAL EXAMINERS: Ms W. Dlamini, Mr S.Jaganath, Mrs S Halstead, Mr R. Webber and Mr E. Zhandire EXTERNAL EXAMINER: Dr J. Govender STUDENT NUMBER SEAT NUMBER THIS PAPER CONSISTS OF 15 PAGES. PLEASE SEE THAT YOU HAVE THEM ALL. IN THEIR OWN INTERESTS, STUDENTS ARE REQUESTED TO: * WRITE LEGIBLY. * CONSULT THE ACCOMPANYING DATA SHEET FOR CONSTANTS AND SOME FORMULAE Multiple Choice Answer Sheet Mark the letter for best answer with a cross as shown below: 1. (A) (B) (C) (D) Question Number Answer (Put a cross over the correct letter) 1. (A) (B) (C) (D) 2. (A) (B) (C) (D) 3. (A) (B) (C) (D) 4. (A) (B) (C) (D) 5. (A) (B) (C) (D) 6. (A) (B) (C) (D) 7. (A) (B) (C) (D) 8. (A) (B) (C) (D) 9. (A) (B) (C) (D) For marking use only

2 SECTION A Multiple Choice [27 Marks] Each question is worth 3 marks. Show your answers on the answer sheet given on the cover. Question 1. Forces F 1 and F 2 are pulling in the directions as shown in the diagram. The equilibrant of these two forces will have the direction: F 1 F 2 A B C D Question 2. Two forces have magnitudes of 30 N and 40 N respectively. Their resultant cannot have a magnitude of: A. 50 N B. 70 N C N D. 80 N Questions 3 and 4 both refer to the following situation: Three point charges of magnitudes -3.0 μc, -3.0 μc and -4.0 μc are placed at the three corners of an equilateral triangle, as shown on the right 3.0 μc 3.0 μc Question 3. The direction of the resultant electrostatic force on the -4.0 μc charge is: A B C D 4.0 μc Question 4. The direction of the resultant electric field at the position of the -4.0 μc charge is: A B C D 2

3 Question 5. The diagram on the right shows three neutral metal spheres, X, Y, and Z, in contact on insulating stands. X Y Z Which diagram best represents the charge distribution on the spheres when a positively charged rod is brought near sphere x, but does not touch it? A. X Y - - Z - B. X Y Z C. X Y - - Z - D. X Y Z Question 6. The diagram on the right shows a free-body diagram of an object being acted upon by 2 vertical forces (Normal force and force of gravity). Three students made the following statements describing the state of motion of the object. Sipho: The object could be stationary. John: The object could be moving vertically at constant velocity. Beauty: The object could be moving horizontally at constant velocity. Which one of the following statements is true? A. Both Sipho and John are correct B. Both John and Beauty are correct C. All three are correct D. Both Sipho and Beauty are correct F N F g 10.0 N 10.0 N Question 7. A force F A = 8.00 N accelerates a box at a = 2.25 m s -2. What would be the new acceleration of the box, if F A is tripled? A m s -2 B m s -2 C m s -2 D m s -2 Question 8. A brick of mass 5.0 kg is pulled vertically upward by a force of 68 N applied to a rope attached to the brick. What is the resultant force on the brick? A. 19 N, upward B. 38 N, upward C. 49 N, downward D. 68 N, upward Question 9. Suppose you press a box against a wall with your hand as illustrated in the diagram on the right. Which one of the following is not an action-reaction pair? A. Force on the earth by the box and force on the hand by the wall. B. Force on earth by the hand and force on the hand by the earth. C. Force on the wall by the box and force on the box by the wall. D. The force of friction on the box by the wall and the force of friction by the wall on the box. 3 [9 x 3]

4 SECTION B Answer the following questions in the spaces provided PROPERTIES OF MATTER [9 marks] Question 10. [9 marks] Convert the following measurements into units shown. Give all answers in scientific notation. (a) m = mm =.n m [3] (b) 25.8 ml = mm 3 =.dm 3 [3] (c) 36 kj = J =.. kwh [3] VECTORS [8 marks] Question 11. [8 marks] Two boys are pulling a box attached to ropes on a frictionless surface, as shown in the diagram. (Take north and east as positive) NORTH F 1 = 450 N bearing 90 F 2 =300 N bearing 145 Use COMPONENTS to calculate the resultant force on the box. [8] 4

5 KINEMATICS [21 MARKS] Question 12. Graphs [12 marks] The graph below shows the motion of an object which started moving northwards when t = 0 s. 8 velocity (m s -1 ) time (s) Answer the following questions from the graph: (a) In what direction was the object travelling between t = 2 s and t = 4 s? [1] (b) At what time did the object first become stationary? [1] (c) At what time did the object have greatest speed? [1] (d) Calculate the acceleration of the object over the period t = 12 s to t = 14 s [4] (e) Describe the motion of the object over the period t = 12 s to t = 14 s. [2] (f) Sketch a position-time graph for the object for the time between 6 s and 10 s [3] x (m) t (s) 5

6 Question 13. Motion in 2-D [8 marks] A stone is thrown horizontally outward from the top of a bridge with an initial velocity 4.96 m s -1. Ignore air resistance. v m If the bridge is 19.6 m above the ground, determine the magnitude and direction of the velocity of the stone just before it strikes the ground. [8] 6

7 DYNAMICS [26 MARKS] Question 14. Newton s first law [8 marks] A block of mass (m) at rest on a frictionless surface is acted on by force F1 10 N and a horizontal force F 2 of unknown magnitude, as illustrated in the diagram on the right. F 2 m F N (a) Determine the magnitude of force F 2. [3] (b) If the normal force acting on the block is 4.8 N, calculate the mass of the block (m). [5] Question 15. Universal law of gravitation [6 marks] A man weighs 750 N on the Earth s surface. How far above the Earth s surface will his weight reduce to 50 % of his weight on the Earth s surface? [6] 7

8 Question 16. Newton s second law [12 marks] A man pushes a box along a rough surface with a force F 300 N, as shown in the diagram on the right. The weight of the box is 98.0 N and the force of friction between the box and the ground is 250 N. F 300 N (a) On the diagram draw in and label all the forces acting on the box. [3] (b) Calculate: (i) the magnitude of the acceleration of the box and, [5] (ii) the magnitude of the force exerted by the ground on the box (the normal force) [4] 8

9 ELECTROSTATICS [20 marks] Question 17. Electrostatics [20 marks] (a) At what distance from charge Q 1 = nc is the magnitude of the electric field 1.85 N C -1? [4] (b) A charged particle of mass 5.0 g remains stationary when placed in a downward directed electric field of magnitude 800 N C -1 (i) On the diagram, draw a force diagram to show the forces acting on the particle. [1] (ii) What is the sign of this charge? show your reasoning. [2] 800 N C g (iii)calculate the magnitude of the charge on the particle. [4] (c) Two charged spheres Y and Z, having charges of 0.70 nc and 12 nc respectively are separated by a distance of 2.0 m. Calculate the resultant force on a µc point Y = 0.70nC 2.0 m X Z = 12nC charge placed at a point X, halfway between the spheres. [6] 9

10 (d) Calculate the energy required to move a 20 µc charge through two points in an electric field, if the potential difference between the points is 6.0 V. [3] CIRCUIT ELECTRICITY [45 marks] Question 18. (11 marks) For the circuit shown below, the current through the ammeter is 120 ma as shown. All the resistors are identical. What will be the current measured at: (f) E A 120 ma A D B C switch (a) A [2] (b) B [2] (c) C [1] (d) D [2] (e) E [1] If the switch is opened what will happen to the ammeter reading at E (increase/decrease/no change)? Explain briefly. [3] Question 19. (10 marks) For the circuit shown below, The voltmeter reading is shown as 3.0 V Write down values for the voltages when a voltmeter is connected across: (f) P Q V 3.0 V R Y T S W (a) RT [2] (b) RY [2] (c) SW [1] (d) WY [1] (e) PY [1] If the lead RS is disconnected, what will be the effect on the voltmeter PQ. Explain briefly. [3] 10

11 Question 20. (9 marks) A battery with emf of 9.00V and unknown internal resistance is connected in the circuit shown in the diagram on the right. The terminal voltage across the battery is 8.70 V and the current through the battery is A. Calculate: (a) The internal resistance. [3] = 9.00 V r I = A R x V = 8.70 V 25.0 Ω 30.0 Ω 70.0 Ω (b) The resistance of resistor R x. [6] 11

12 6.00 V 1.00 A 4.00 Ω 1.25 A Question 21. (15 marks) For the circuit shown below, you may neglect the resistance of the batteries and connecting leads. Refer to the appropriate nodes and loops in your calculations. I x Node a Loop 3 Loop 1 Loop 2 R x V x Ω Node b Calculate the following: (a) Current I x. [2] (b) Resistance R x. [5] (c) Battery voltage, V x. [3] (d) The energy transferred when current flows for 2 hours through the 4.00 Ω resistor. [5] 12

13 OPTICS [25 marks] Question 22. Reflection (5 marks) A student of height 1.70 m (and eyes 0.16 m from the top of her head) stands 2.00 m away from a plane (straight) mirror, as shown in the diagram below (a) How far is the image of the student from the mirror? [1] (b) What is the height of the student s image in the mirror? [1] (c) If the bottom of the mirror is 0.77 m from the floor, will the student be able to see her feet in the mirror? Explain your reasoning by completing a labelled diagram below, or with a calculation. [3] SCALE: 1 cm represents 0.5 m or 1:50 eyes 0.16 m below top of head height 1.70 m mirror 2.00 m away from mirror Height of mirror off ground = 0.77 m 13

14 Question 23. Refraction (11 marks) A ray of light in a material with refractive index 1.30 strikes an interface with air at an angle of 35.5º to the surface of the material. (a) What does the refractive index tell us about the material? [2] (b) Use the space below to draw the incident ray, the normal to the surface of the material and the refracted ray. Clearly mark the angle of incidence in your diagram. [2] air material, n = 1.30 (c) By calculation, determine whether this light would be refracted or be totally internally reflected? [7] 14

15 Question 24. Lenses (9 marks) An object is placed 5.8 cm to the left of a converging lens as shown below. It forms a sharp image on the screen 9.0 cm from the lens as shown below. (a) Will the image be real or virtual? Explain your reasoning. [2] (b) On the diagram show how the two light rays drawn would pass through the lens. In your diagram you should clearly draw the image and mark the focal points. [4] Screen position Object (c) Use your completed diagram to measure the focal length of the lens and verify this by calculation. [3] TOTAL 180 marks 15