Physics 2204 UNIT 2 Exam: Forces and Newton s Laws

Transcription

1 Physics 2204 UNIT 2 Exam: Forces and Newton s Laws Time: 60 minutes Total Value: 35 marks Formulae and Constants: + - V = = a = av t d tot V1 V 2 V 2 V1 V av tot 2 t d = Vt 1 + 2at d = V2t 2at 2ad = V 2 - V1 F Net = ma F = F + F F = μ F net app fr fr N F A on B = F Felastic = kδx B on A mm FG = G g = 9.8 G = d m/ N m /kg 2 s SECTION A Instructions: Do not place answers on this paper - use the answer sheet to be found on p. 6 of this test. For questions 1 25 put the appropriate letter in the blanks. {1 mark each} 1. An object on Earth has a mass of 20.0 kg. What is its weight in Newton s? (A) 0.49 N (C) 9.8 N (B) 2.04 N (D) 196 N 2. If you are in a spacecraft moving away from the Earth what is happening? (A) Both your mass and your weight are increasing. (B) Both your mass and your weight are decreasing. (C) Your mass decreases while your weight remains constant. (D) Your weight decreases while your mass remains constant. 3. F 2 = 200 N [20 o N of W] Which choice correctly describes the signs of the components of F 2. (A) both are positive (B) both are negative (C) F 2x is positive and F 2y is negative (D) F 2x is negative and F 2y is positive Physics 2204 Unit 2 Exam Page 1 of 7

2 4. What is the net unbalanced force on the car in the picture. (A) 400 N (C) 400 N (B) 200 N (D) 500 N 5. A force of 100 N acts on an object. In which instance are the horizontal and vertical components equal? (A) The force acts at an angle of 0 o above the horizontal. (B) The force acts at an angle of 45 o above the horizontal. (C) The force acts at an angle of 90 o above the horizontal. (D) The horizontal and vertical components cannot be equal. 6. Two force vectors F 1 and F 2 are added. Which diagram correctly shows the vectors added to produce the resultant? 7. Suppose that two equal forces act on the same object. Under which condition does the resultant have zero magnitude? (A) never (B) the forces act at right angles to one another (C) the forces act at 45 o angles to one another (D) the forces act in opposite directions 8. Suppose that a force of 20.0 N will stretch a horizontal spring 1.0 cm from its rest position. What force will stretch the spring 2.0 cm from its rest position? (A) 10 N (B) 40 N (C) 80 N (D) 160 N Physics 2204 Unit 2 Exam Page 2 of 7

3 9. A spring is stretched some distance using a force. How are the values of force and stretch related? They are... (A) in direct proportion (C) equal (B) in inverse proportion (D) unrelated 10 A spring has a spring constant k = N/m. An applied force of 5.2 N will stretch it how far from the rest position? (A) m (B) 38.5 m (C) 38.5 cm (D) 1040 m 11. Suppose that you sat on a high performance snowmobile and briefly pushed the throttle to full power. What physical principle would be demonstrated as your head snapped backward as the machine underwent enormous acceleration? (A) Newton s 1st Law (C) Newton s 3rd Law (B) Newton s 2nd Law (D) Law of Equilibrant Forces 12. Which situation is best explained using Newton s Second Law of Motion? (A) Dust is removed from a cloth by shaking it. (B) A care package released from a plane at a height of 200 m lands on the target just as the plane flies over the target. (C) A cassette tape resting on the dash of a car slides to the right as the car makes a sharp turn to the left. (D) A train requires a larger force to accelerate it than does a bicycle. 13. An inflated balloon will fly away as the air escapes. What is this an illustration of? (A) Law of Universal Gravitation. (B) Second Law of Motion (C) First Law of Motion (D) Third Law of Motion 14. Imagine that you shoot a hockey puck on a wide, frozen lake that is covered by perfectly frictionless ice. If there is no air resistance (or any other opposing force), then what will happen to the puck? (A) It will continue to move at a constant speed until it reaches the far shore. (B) It will very gradually slow down. (C) It will come to rest quickly. (D) It will very gradually speed up. Physics 2204 Unit 2 Exam Page 3 of 7

4 15. Which choice represents an inertial frame of reference? (A) in an aircraft accelerating for takeoff (B) in an aircraft in level flight (C) in an aircraft bumping up and down in rough weather (D) all of the above are inertial frames of reference 16. A 1.0 kg ball is rolling on a frictionless horizontal floor at a constant velocity of 2.0 m/s. What is the net force on the object? (A) 0.0 N (B) 2.0 N (C) 4.0 N (D) 19.6 N 17. Suppose that the force that presses two surfaces together is doubled. What happens to the frictional force between the two surfaces? (A) decreased by a factor of 2 (B) increased by a factor of 2 (C) increased by a factor of 4 (D) the same (unchanged) 18. A boy is holding a basketball as shown. There are two forces on the ball (F1 & F2) and three forces on the boy (F3, F4, & F5) which may be described as follows: F 1 = the earth's gravitational force on the ball F 2 = the force that the hands exerts upward on the ball F 3 = the force the ball is pushing down on the hands F 4 = the earth's gravitational force on the boy F 5 = the force that the earth is pushing back on the boy Which choice represents an action-reaction pair? (A) F 1 & F 2 (B) F 2 & F 3 (C) F 3 & F 4 (D) F 4 & F A 1.0 kg ball is rolling on a frictionless horizontal floor at a constant velocity of 2.0 m/s. What is the net force on the object? (A) 0.0 N (B) 2.0 N (C) 4.0 N (D) 19.6 N 20 At full throttle a certain snowmobile can apply a constant force to a sled loaded with wood. If the sled and snowmobile have a mass of 500 kg the acceleration will be 2 m/s 2. If the total mass is increased to 1000 kg, what will be the acceleration? (A) 0.5 m/s 2 (B) 1 m/s 2 (C) 2 m/s 2 (D) 4 m/s 2 Physics 2204 Unit 2 Exam Page 4 of 7

5 21. A net force of 32 N is applied to a mass of 200 g. What is the resulting acceleration? (A) m/s 2 (B) 0.16 m/s 2 (C) 6.4 m/s 2 (D) 160 m/s A force of 55.0 N is applied to push a box of mass 20.0 kg across a table. If there is a frictional force of 10.0 N between the table and the box, what is the resulting acceleration of the box? (A) 2.25 m/s 2 (B) 2.75 m/s 2 (C) 3.25 m/s 2 (D) 45 m/s A wagon loaded with newspapers has a mass of 22.5 kg. It is being pulled using the handle which makes an angle of 40.0º above the horizontal with an applied force of 82.5 N. What is the effective weight of the wagon? (A) 53 N (B) 168 N (C) 221 N (D) 274 N 24. Two objects, each having a mass of kg, are separated by a distance of m. What is the gravitational force between them? (A) N (B) N (C) 0.39 N (D) 1200 N 25. Two objects in deep space experience a gravitational attraction of 400 N. What would be the gravitational force between the objects if the mass of one object were tripled and the distance between their centres was reduced to one-half? (A) 600 N (B) 1200 N (C) 2400 N (D) 4800 N Physics 2204 Unit 2 Exam Page 5 of 7

6 Name: Site: p of Physics 2204 Unit 2 Test Answer Sheet for Section A Print your Choice Clearly SECTION B Instructions: Place your answers and solutions in the spaces provided. {3} 26. Use a method of your choice to find the resultant of the following three forces if they act on the same point. F 1 = N [30.0 º E of S] F 2 = N [N] F 3 = N [W] Physics 2204 Unit 2 Exam Page 6 of 7

7 Name: Site: p of Physics 2204 Unit 2 Test {3} 27. A driver in a car notices that, at full power, with a net force of 900 N, it accelerates at 2.0 m/s 2. Suppose that car takes on passengers with a combined extra mass of kg. What will be the acceleration of the loaded car at full power? {3} 28. A 10.0 kg block is on a horizontal table. The coefficient of friction between the block and the table is It is connected to a 5.0 kg hanging mass by a lightweight string and a pulley as shown. Ignore the mass of the string and any friction in the pulley. Calculate the acceleration of the 10.0 kg block across the table top. μ = kg 5.0 kg Physics 2204 Unit 2 Exam Page 7 of 7