Name: Class: Date: Fall 2012 Physics Quiz 4--Introduction to Forces

Transcription

1 Name: Class: Date: ID: A Fall 2012 Physics Quiz 4--Introduction to Forces Please do not write on these pages. MC: 1pt each + FR 6pt each = 50 points possible. Multiple Choice Identify the choice that best completes the statement or answers the question. 1. (1 point) Which of the following is the cause of an acceleration? a. speed b. inertia c. force d. velocity 2. (1 point) Which of the following statements does not describe force? a. Force causes objects at rest to remain stationary. b. Force causes objects to start moving. c. Force causes objects to stop moving. d. Force causes objects to change direction. 3. (1 point) What causes a moving object to change direction? a. acceleration b. velocity c. inertia d. force 4. (1 point) Which of the following forces arises from direct physical contact between two objects? a. gravitational force b. fundamental force c. contact force d. field force 5. (1 point) A newton is equivalent to which of the following quantities? a. kg b. kg m/s c. kg m/s 2 d. kg (m/s) 2 6. (1 point) The length of a force vector represents the a. cause of the force. b. direction of the force. c. magnitude of the force. d. type of force. 7. (1 point) Which of the following is the tendency of an object to maintain its state of motion? a. acceleration b. inertia c. force d. velocity 8. (1 point) A car goes forward along a level road at constant velocity. The additional force needed to bring the car into equilibrium is a. greater than the normal force times the coefficient of static friction. b. equal to the normal force times the coefficient of static friction. c. the normal force times the coefficient of kinetic friction. d. zero. 9. (1 point) As an object falls toward Earth, a. the object does not exert a force on Earth. b. the object exerts a downward force on Earth. c. Newton s third law does not apply. d. the upward acceleration of Earth is negligible because of its large mass. 10. (1 point) If a nonzero net force is acting on an object, then the object is definitely a. at rest. b. moving with a constant velocity. c. being accelerated. d. losing mass. 11. (1 point) In general, et equals a. F f. b. F g. c.. d. ΣF. 12. (1 point) A net force of 6.8 N accelerates a 31 kg scooter across a level parking lot. What is the magnitude of the scooter s acceleration? a m/s 2 b m/s 2 c. 3.2 m/s 2 d. 4.6 m/s (1 point) The statement by Newton that for every action there is an equal but opposite reaction is which of his laws of motion? a. first b. second c. third d. fourth 14. (1 point) Which are simultaneous equal but opposite forces resulting from the interaction of two objects? a. net external forces b. field forces c. gravitational forces d. action-reaction pairs 1

2 Name: ID: A 15. (1 point) A hammer drives a nail into a piece of wood. Identify an action-reaction pair in this situation. a. The nail exerts a force on the hammer; the hammer exerts a force on the wood. b. The hammer exerts a force on the nail; the wood exerts a force on the nail. c. The hammer exerts a force on the nail; the nail exerts a force on the hammer. d. The hammer exerts a force on the nail; the hammer exerts a force on the wood. 16. (1 point) The magnitude of the gravitational force acting on an object is a. frictional force. b. weight. c. inertia. d. mass. 17. (1 point) A measure of the quantity of matter is a. density. b. weight. c. force. d. mass. 18. (1 point) In a coordinate system, a vector is oriented at angle θ with respect to the x-axis. The x component of the vector equals the vector s magnitude multiplied by which trigonometric function? a. cos θ b. cot θ c. sin θ d. tan θ 19. (1 point) In a coordinate system, a vector is oriented at angle θ with respect to the x-axis. The y component of the vector equals the vector s magnitude multiplied by which trigonometric function? a. cos θ b. cot θ c. sin θ d. tan θ 20. (1 point) According to Newton s second law, when the same force is applied to two objects of different masses, a. the object with greater mass will experience a great acceleration, and the object with less mass will experience an even greater acceleration. b. the object with greater mass will experience a smaller acceleration, and the object with less mass will experience a greater acceleration. c. the object with greater mass will experience a greater acceleration, and the object with less mass will experience a smaller acceleration. d. the object with greater mass will experience a small acceleration, and the object with less mass will experience an even smaller acceleration. Problems. Draw a diagram for each problem. Draw a Free Body diagram when appropriate. Show all your work, including the equation(s) you will use. 21. (6 points) While grazing, a caribou treks 125 m at 35.0 west of south, and then 105 m west. What is the caribou s resultant displacement? 22. (6 points) A model rocket flies horizontally off the edge of a cliff at a velocity of 50.0 m/s. If the canyon below is m deep, how far from the edge of the cliff does the model rocket land? (a y = g = 9.81 m/s 2 ) 23. (6 points) Basking in the sun, a 1.10 kg lizard lies on a flat rock tilted at an angle of 15.0 with respect to the horizontal. What is the magnitude of the normal force exerted by the rock on the lizard? 24. (6 points) A three-tiered birthday cake rests on a table. From bottom to top, the cake tiers weigh 16 N, 9 N, and 5 N, respectively. What is the magnitude and direction of the normal force acting on the second tier? 25. (6 points) A waitperson pushes the bottom of a glass tumbler full of water across a tabletop at constant speed. The tumbler and its contents have a mass of 0.70 kg, and the coefficient of kinetic friction for the surfaces in contact is What force does the waitperson exert on the glass? g = 9.81 m/s 2 ) 2

3 Fall 2012 Physics Quiz 4--Introduction to Forces Answer Section MULTIPLE CHOICE 1. ANS: C PTS: 1 DIF: I OBJ: ANS: A PTS: 1 DIF: I OBJ: ANS: D PTS: 1 DIF: I OBJ: ANS: C PTS: 1 DIF: I OBJ: ANS: C PTS: 1 DIF: I OBJ: ANS: C PTS: 1 DIF: I OBJ: ANS: B PTS: 1 DIF: I OBJ: ANS: D PTS: 1 DIF: I OBJ: ANS: D PTS: 1 DIF: II OBJ: ANS: C PTS: 1 DIF: I OBJ: ANS: D PTS: 1 DIF: II OBJ: ANS: A F applied = 6.8 N m = 31 kg et = a x = F applied m F x = F applied = ma x = 6.8 N 31 kg.22 m/s2 PTS: 1 DIF: IIIA OBJ: ANS: C PTS: 1 DIF: I OBJ: ANS: D PTS: 1 DIF: I OBJ: ANS: C PTS: 1 DIF: II OBJ: ANS: B PTS: 1 DIF: I OBJ: ANS: D PTS: 1 DIF: I OBJ: ANS: A PTS: 1 DIF: I OBJ: ANS: C PTS: 1 DIF: I OBJ: ANS: B PTS: 1 DIF: II OBJ:

4 PROBLEM 21. ANS: 204 m, 59.9 west of south d 1 = 125 m d 2 = 105 m θ 1 = 35.0 west of south θ 2 = 90.0 west of south x 1 = d 1 sinθ 1 = (125 m)(sin35.0 ) = 71.8 m y 1 = d 1 cosθ 1 = (125 m)(cos35.0 ) = 102 m x 2 = 105 m y 2 m x tot = x 1 + x 2 = 71.8 m m = 177 m y tot = y 1 + y 2 m m = 102 m d = ( x tot ) 2 + ( y tot ) 2 = (177 m) 2 + (102 m) 2 = 204 m Ê θ = tan m ˆ Ë Á 102 m = 59.9 d = 204 m, 59.9 west of south PTS: 6 DIF: IIIC OBJ:

5 22. ANS: 226 m v = 50.0 m/s horizontally y = m v i, x = v x = 50.0 m/s v i, y y = 1 2 a y ( t)2 ( t) 2 = 2 y a y t = 2 y a y = 2( m) ( 9.81 m/s 2 ) = 4.52 s x = v x t = (50.0 m/s)(4.52 s) = 226 m PTS: 6 DIF: IIIB OBJ: ANS: 10.4 N m = 1.10 kg θ = 15.0 g = 9.81 m/s 2 et, y = ΣF y = F g, y = F g, y = F g cosθ = mgcosθ = (1.10 kg)(9.81 m/s 2 )(cos15.0 ) = 10.4 N PTS: 6 DIF: IIIA OBJ:

6 24. ANS: 14 N, upward F g, 1 = 5 N F g, 2 = 9 N F g, 3 = 16 N et, y = ΣF y = F g, 1 F g, 2 = F g, 1 + F g, 2 = 5 N + 9 N = 14 N = 14 N, upward PTS: 6 DIF: IIIA OBJ: ANS: 2.8 N m.70 kg µ k.41 g = 9.81 m/s 2 et, y = F g = F g et, x = F applied F f F applied = F f F f = µ k = µ k F g = µ k mg = ( 0.41)(0.70 kg)(9.81 m/s 2 ) = 2.8 N F applied = F f = 2.8 N PTS: 6 DIF: IIIA OBJ: