phymid2 - Simon Fraser University Physics 101 Fall 2008...

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Unformatted text preview: Simon Fraser University Physics 101 Fall 2008 Midterm Exam 1 - A Friday, October 3, 2008 Time allowed: 50 minutes Last Name:________________________ First Name:________________________ SFU Stud ID #:_____________________ Instructions: Please write your name and student number and fill it in on the optically readable scan cards given to you for your responses to questions in Part I. No books or aids other than the formula sheet provided in this exam are allowed. Only Aurex SC 6108 or Aurex 6145 calculators are permitted. No cellphones or PDA’s are permitted to be out during the examination. No communication of any sort with other students nor looking at other student’s papers is permitted during the examination and will result in a mark of zero and possible further disciplinary action by the University. Part I : Multiple Choice Questions: 5 marks each Answer all questions. Please carefully fill in the box corresponding to the correct answer on the optically readable cards. No credit will be given for answers circled on this sheet. Q1. A spring stretched by an amount d is used to pull an object of mass M and it accelerates the mass at 2 m/s2. If the same spring is now stretched by an amount 4d and used to accelerate another object of mass 2M the acceleration will now be: (A) 1 m/s2 (B) 2 m/s2 (C) 4 m/s2 (D) 8 m/s2 (E) 16 m/s2 Q2. A 730 kg Smart car undergoes a head-on collision with a 5000 kg truck. Which of the following is true? A) The force the truck exerts on the Smart car is greater than the force the Smart car exerts on the truck. B) The forces the two vehicles exert on each other are equal in magnitude. C) The force the truck exerts on the Smart car is smaller than the force the Smart car exerts on the truck. D) You cannot determine a relationship between the two forces. E) None of the above Q3. A lamp of mass m hangs from a spring scale that is attached to the ceiling of an elevator. When the elevator is stopped at the fortieth floor, the scale reads mg. What does it read while the elevator descends toward the ground floor at a constant speed? (A) More than mg. (B) mg (C) Less than mg. (D) Zero. (E) This cannot be answered without knowing how fast the elevator is descending. Q4. A ball is swung around on the end of a string at constant speed in the direction indicated by the arrows. The diagram shows the path of the ball in the horizontal plane as viewed from above while the person is holding the string. If the person lets go of the string when the ball is in the position shown, in which direction in the horizontal plane will the ball fly off ? B) C) D) E) A) Q5. An object moving along the x-axis has a position x = +3 m and is moving with a velocity of -4 m/s. The object is slowing down, that is, its speed is decreasing. The sign of its acceleration is: (A) 0 (B) negative (C) positive (D) <0 until it stops, then >0 (E) impossible to tell Part II: Problems : 25 marks each Please complete on the midterm exam sheet itself. Show your work. Answer all questions. Problem 1 A basketball player shoots and makes a basket by launching the ball from a height of 2.4m above the floor and 12.81 m away horizontally (measured from centre of ball to centre of basket) at a speed of 12 m/s at an angle of 350 above the horizontal as depicted below. The height of the centre of the hoop (of the basket) is at 10 feet = 3.05 m above the floor. d = 12.81m A) How much time does it take for the basketball to enter the basket starting from the time that the shot is taken? ( 12 marks) B) At what angle does the basketball enter the basket, that is, what is the angle that the velocity vector of the basketball makes with the horizontal at the instant the basketball enters the basket ? (13 marks) Problem 2 A wooden block of mass m=2 kg begins to slide with an initial speed of 3 m/s up from the bottom of a wooden incline plane that makes an angle of = 300 with the horizontal. The coefficient of static friction for wood sliding on wood is s = 0.4, and the coefficient of kinetic friction for wood sliding on wood is k = 0.2. Neglect drag. A) What is the distance, d, up the incline that the block slides before it stops ? (15 marks) B) Once it stops does the block begin to slide back down ? Show calculations.(10 marks) Problem 3 A locomotive is pushing a boxcar of mass M= 200 kg, height h= 6m, width w= 4m, and length l = 10 m, at a constant velocity of v=60 km/hour. It is pushing it with its front bumper which is a hefty spring of spring constant k = 2 x 107N/m. The density of air is 1.29 kg / m3. Assume that the front surface of the boxcar is the relevant area for the purpose of calculating the drag force on it and that the locomotive experiences zero drag force since it is immediately behind the boxcar. A) What is the force that the locomotive is delivering ? (12 marks) B) By how much is the front bumper spring of the locomotive compressed ? (13 marks) Kinematics Newton’s Laws Centripetal Acceleration Gravitational Field and Acceleration on Earth Gravitational Force on Earth Force exerted by a spring Frictional force Linear Drag Force on a Sphere Quadratic Drag Force ...
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