Physics Mid-Term Practice Exam Multiple Choice. Identify the choice that best completes the statement or answers the question. 1. Which one of the following problems would NOT be a part of physics? a. Calculating the average density of a person b. Calculating the amount of energy a person uses while listening to a lecture c. Calculating the instantaneous velocity of an accelerating car d. Identifying all the forces acting on a person who is walking uphill e. Identifying all the bones in a human body 2. A hypothesis is a. the long side of a right triangle. b. an educated guess that has yet to be proven by experiment. c. close agreement by competent observers of observations of the same phenomena. d. a guess that has been tested over and over again and always found to be true. e. a synthesis of a large collection of information that includes guesses. 3. The amount gravitational potential energy increases when an object is elevated is equal to a. the power used to lift it. d. the work done in lifting it. b. the distance it is lifted. e. the value of the acceleration due to gravity. c. the force needed to lift it. 4. Energy is changed from one form to another with no net loss or gain. a. Sometimes true b. Always false c. Always true 5. When a car s speed triples, which energy storage mechanism increases? a. elastic potential energy d. kinetic energy b. chemical energy e. gravitational potential energy c. thermal energy 6. As an object s temperature increases, the increased energy is stored by which mechanism? a. elastic potential energy d. kinetic energy b. chemical energy e. gravitational potential energy c. thermal energy 7. An object at rest does not store energy as a. kinetic energy. b. gravitational potential energy. c. thermal energy. 8. Heat travels from the sun to Earth by a. conduction. b. radiation. c. convection. d. elastic potential energy. e. chemical energy. d. insulation. e. vacuumization. 9. When you look at the speedometer in a moving car, you can see the car's a. average distance traveled. d. instantaneous speed. b. instantaneous acceleration. e. average acceleration. c. average speed.
10. A car starts from rest and after 7 seconds it is moving at 42 m/s. What is the car s average acceleration? a. 0.17 m/s 2 d. 7 m/s 2 b. 1.67 m/s 2 e. none of the above c. 6 m/s 2 11. In the absence of air resistance, objects fall at constant a. speed. d. distances each successive second. b. velocity. e. all of the above c. acceleration. 12. A ball tossed vertically upward rises, reaches its highest point, and then falls back to its starting point. During this time the acceleration of the ball is always a. in the direction of motion. c. directed downward. b. opposite its velocity. d. directed upward. 13. Suppose you take a trip that covers 180 km and takes 3 hours to make. Your average speed is a. 30 km/h. d. 360 km/h. b. 60 km/h. e. 540 km/h. c. 180 km/h. 14. A ball is thrown straight up. At the top of its path its acceleration is a. 0 m/s 2. d. about 20 m/s 2. b. about 5 m/s 2. e. about 50 m/s 2. c. about 10 m/s 2. 15. If a ball were equipped with a speedometer and allowed to fall freely on a planet where the acceleration due to gravity is 23 m/s 2, the reading on the speedometer would increase each second by a. a rate that depends on its initial speed. b. 10 m/s. c. 12 m/s. d. 23 m/s. e. 46 m/s. 16. The vertical height attained by a basketball player who achieves a hang time of a full one second is about a. 0.8 m. d. 2.5 m. b. 1 m. e. more than 2.5 m. c. 1.2 m. 17. A pencil lies on your desk. If the Earth is moving around the sun at a speed of 30 km/s, how fast is the pencil moving relative to the desk? How fast is the pencil moving relative to the sun? a. 0 km/s; 0 km/s b. 0 km/s; 30 km/s c. 30 km/s; 30 km/s d. There is not enough information to answer these questions. 18. What is the maximum resultant possible when adding a 2-N force to an 8-N force? a. 2 N d. 10 N b. 6 N e. 16 N c. 8 N
19. Equilibrium occurs when a. all the forces acting on an object are balanced. b. the sum of the +x forces on an object equals the sum of the x forces. c. the net force on the object is zero. d. the sum of the upward forces equals the sum of the downward forces. e. all of the above 20. A 100-N lantern is suspended by a pair of ropes with 120 degrees between them (each 60 degrees from the vertical). The tension in each rope is a. less than 100 N. b. more than 100 N. c. 100 N. 21. A scalar quantity has a. only direction. b. only magnitude. c. both magnitude and direction. d. neither magnitude nor direction. 22. Friction a. comes from microscopic bumps that act as obstructions to the object's motion. b. is the name given to the force acting between surfaces sliding past one another. c. acts in a direction that opposes the motion of an object. d. all of the above e. none of the above 23. Compared to its weight on Earth, a 10-kg object on the moon will weigh a. the same amount. b. less. c. more. 24. You would have the largest mass of gold if your chunk of gold weighed 1 N on a. Earth. b. Jupiter. c. the moon. 25. How much does a 3.0-kg bag of bolts weigh? a. 7.2 N b. 14.4 N c. 22.8 N d. 29.4 N e. 58.8 N 26. A vector is a quantity that has a. magnitude and time. b. time and direction. c. magnitude and direction. 27. When representing velocity as a vector, a. the direction of the arrow shows the direction of d. motion. all of the above b. the length of the arrow represents the speed. e. none of the above c. the length of the arrow is drawn to a suitable scale. 28. In the absence of air friction, the vertical component of a projectile's velocity doesn't change as the projectile moves. a. Always false b. Always true c. Sometimes true
29. At the instant a ball is thrown horizontally with a large force, an identical ball is dropped from the same height. Which ball hits the ground first? a. Neither. They both hit the ground at the same time. b. The dropped ball c. The horizontally thrown ball 30. A ball thrown in the air will never go as far as physics ideally would predict because a. one can never throw the ball fast enough. d. ideally the ball would never land. b. gravity is acting. e. all of the above c. air friction slows the ball. 31. A cannonball is launched from the ground at an angle of 30 degrees above the horizontal and a speed of 30 m/s. Ideally (no air resistance) the ball will land on the ground with a speed of a. 0 m/s. d. 40 m/s. b. 20 m/s. e. There is not enough information to say. c. 30 m/s. 32. Which best approximates the resultant of a pair of 6-unit vectors at right angles to each other? a. 0 units. c. 8 units. b. 6 units. d. 12 units. 33. The air in your classroom has _. a. mass b. energy c. weight d. all of the above e. none of the above 34. An object has a constant mass. A constant force on the object produces constant a. velocity. c. both A and B b. acceleration. d. none of the above 35. If a truck has ten times the mass of a car and the two vehicles are pushed with an equal force, you would expect the acceleration of the truck to be a. one-tenth that of the car. b. one-hundredth that of the car. c. 10 times that of the car. d. 100 times that of the car. 36. An archer shoots an arrow. Consider the action force to be the bowstring against the arrow. The reaction to this force is the a. arrow's push against the bowstring. b. weight of the arrow. c. friction of the ground against the archer's feet. d. air resistance against the bow. e. grip of the archer's hand on the bow. 37. The reason a tennis ball and a solid steel ball will accelerate at the same rate, in the absence of air resistance, is that a. they have the same mass. b. the ball with the larger force has the smaller mass. c. the ball with the larger force also has the larger mass. d. the force acting on them is the same. e. none of the above 38. A player hits a ball with a bat. The action force is the impact of the bat against the ball. What is the reaction to this force? a. The force of the ball against the bat d. The grip of the player's hand against the bat b. The weight of the ball e. none of the above c. Air resistance on the ball
True/False. Indicate whether the statement is true or false. Fix it if it is false. 39. In science, an educated guess and explanation about the answer to a problem is called a hypothesis. 40. The unit of work is called the joule. 41. The energy an object has by virtue of its motion is its kinetic energy. 42. The rate at which distance is covered is called speed. 43. Velocity is different from speed in that velocity is speed in a given direction. 44. When a car rounds a corner at a constant speed, its acceleration is zero. 45. A ball is thrown into the air. At the highest point, the ball has zero velocity and zero acceleration. 46. Mass is a vector quantity. 47. A force can be simply defined as a push or a pull. 48. If you were to slide a hockey puck across a frictionless ice rink, there must be a horizontal force on it to keep it in motion. 49. An astronaut has the same mass on Earth as in space. 50. A quantity that has both magnitude and direction is called a scalar. 51. The length of a vector represents its magnitude. 52. Any vector can be represented by two other vectors that are at right angles to each other.
Essay 53. Why is physics considered the basic science? 54. Write a short paragraph on the key points of any scientific process. 55. Make a table that show the quantities we ve studied so far in this class, their symbol, the SI Unit of measurement, and indicate whether it s a base unit or derived unit.
56. Discuss how energy conservation applies to a pendulum. Where is gravitational potential energy the most? The least? Where is kinetic energy the most? The least? Where is it moving the fastest? Stopped? How does its mechanical energy change throughout its motion? 57. Write a short paragraph explaining the difference between speed and velocity, and give examples of both. 58. Write a short paragraph explaining what acceleration is and why a car is accelerating as it rounds a corner. Problem 59. A block of wood has a mass of 40.0 g and a volume of 95.2 cm 3. What is its density?
60. A block of wood has a mass of 589 g with a width of 8.75 cm and a depth of 3.85 cm. If the wood has a density of 745 kg/m 3 what is the length of the wood block? 61. You expend 1550 J of energy lifting a package from the floor to a shelf. By how much did the package s gravitational potential energy increase? 62. A jet on an aircraft carrier can be launched 42.0 meters in 1.5 seconds. What is the acceleration of the jet? 63. You toss a ball at 5 m/s straight upward. How long will it take the ball take to reach the top of its path? 64. What vertical distance can a person with a 0.7 s hang time jump?
65. A crate falls from an airplane flying horizontally at an altitude of 1250 m. Neglecting air drag, how long will the crate take to strike the ground? 66. What is the resultant force vector of a 6.0-N force acting vertically upward and a 4.0-N force acting horizontally? 67. On the moon, the acceleration due to gravity is one-sixth that on Earth. What would be the weight of 0.9 kg of bologna on the moon? 68. Consider an escalator at an angle of 40.0 above the horizontal that moves with a velocity of 2.50 m/s. What is the vertical component of the escalator's velocity? 69. A ball is thrown upward. Its initial vertical component of velocity is 30.0 m/s and its initial horizontal component of velocity is 10.0 m/s. What is the ball's speed 4.00 s later?
70. A cannonball is launched at an angle of 38.5 and has an initial velocity of 755 m/s. What is the range of the cannonball? Assume air resistance in negligible and the ball lands at the same elevation it was launched from. 71. A ball is thrown at an angle of 45.0. What must the ball s initial velocity be in order to hit a target 25.0 m above the launch point when it is at the peak of its trajectory? Assume air resistance is negligible. 72. A 45.5kg person is hanging from a 1.00kg trapeze bar by one hand. Draw a free body diagram showing the force vectors acting where the person s hand contacts the bar, and where the cables are attached at the ends of the bar. The cables are perpendicular to the bar. 73. A 55.5 kg skydiver with a 12.5 kg harness and parachute reaches terminal (constant) velocity just before she opens her parachute. Draw a free body diagram showing the force vectors that exist on the skydiver.
74. Suppose that you exert 300 N horizontally on a 50-kg crate on a factory floor, where friction between the crate and the floor is 100 N. What is the acceleration of the crate? 75. A 25.0-kg crate slides down a 30.0º frictionless ramp. What is the acceleration of the crate?
Physics Mid-Term Practice Exam - Answer Section MULTIPLE CHOICE 1. ANS: E 2. ANS: B 3. ANS: D 4. ANS: C 5. ANS: D 6. ANS: C 7. ANS: A 8. ANS: B 9. ANS: D 10. ANS: C 11. ANS: C 12. ANS: C 13. ANS: B 14. ANS: C 15. ANS: D 16. ANS: C 17. ANS: B 18. ANS: D 19. ANS: E 20. ANS: C 21. ANS: B 22. ANS: D 23. ANS: B 24. ANS: C 25. ANS: D 26. ANS: C 27. ANS: D 28. ANS: A 29. ANS: A 30. ANS: C 31. ANS: C 32. ANS: C 33. ANS: D 34. ANS: B 35. ANS: B 36. ANS: A 37. ANS: C 38. ANS: A
TRUE/FALSE 39. ANS: T 40. ANS: T 41. ANS: T 42. ANS: T 43. ANS: T 44. ANS: F 45. ANS: F 46. ANS: F 47. ANS: T 48. ANS: F 49. ANS: T 50. ANS: F 51. ANS: T 52. ANS: T ESSAY 53. ANS: Physics is about the basic nature of things such as motion, matter, and energy. Physics underlies the science of chemistry, which is a study of how matter is put together. Chemistry, in turn, underlies biology and the life sciences. Physics, therefore is the basic science. 54. ANS: The scientific method involves making some sort of educated guess about the solution to a problem, devising an experiment to test this guess, gathering data, analyzing the data, and forming a generalization based on results of your data. For example, we use the scientific method when we conclude that the moon affects ocean tides, or that liquids will turn to gases when heated sufficiently. The scientific method generally is used to make rules about the nature of things. 55. ANS: This table should include time (second, base), distance (meter, base), displacement (meter, base), position (meter, base), velocity (meter per second, derived), acceleration (meter per second squared, derived), mass (kilogram, base), and force (Newton or kilogram times meter per second square, derived). 56. ANS: Net energy is never created or destroyed. It can change from one form to another form. A swinging pendulum has the most gravitational potential energy at the top of its swing. At that point it has no kinetic energy. At the bottom of its swing its potential energy is at a minimum, or zero relative to that lowermost point, and its kinetic energy is at a maximum. Halfway down, it has half kinetic and half gravitational potential energy. Everywhere along the swing the sum of the kinetic and potential energies is the same, hence its mechanical energy is constant. When air resistance and friction are taken into account, energy is transferred from the pendulum to the surroundings in the form of heat. 57. ANS: Speed is the rate at which an object covers distance. Velocity is speed in a direction. When you get in a car and travel on a highway at 90 km/hr that is your speed. If you are traveling south, then your velocity is 90 km/h S. 58. ANS: Acceleration is the rate of change of velocity. Since velocity has both speed and direction, if the direction of a moving object changes, as in rounding a corner, then the object is accelerating.
PROBLEMS 59. ANS: D = m V 40.0 g = 1 kg (100 cm)3 = 420. kg 95.2 cm 3 1000 g (1 m) 3 m 3 60. ANS: D = m V = m l w d l = m D w d = 589 g 1 kg (745 kg m 3)(8.75 cm)(3.85 cm) 1000 g 61. ANS: Law of Conservation of Energy, therefore 1550 J. 62. ANS: d = 1 2 at2 +V 0 t and v 0 = 0 a = 2d t 2 63. ANS: v = at+v 0, at the ball s peak v = 0, so t = v 0 2(42.0 m) = = 37 m (1.5 s) 2 s 2 = 5 m s a 9.81 m s 2 = 0.5 s (100 cm)2 (1 m) 2 = 0.235 m 64. ANS: if we study the downward portion of the jump, which will take ½ the total, hang-time, d = 1 2 at2 +V 0 t = 1 ( 9.81 m 2 s of the jump. 2) (0.7 s 2 )2 = 0.6 m, distance is negative because it s the downward portion 65. ANS: d = 1 2 at2 +V 0 t and v 0 = 0 t = 2d = 2( 1250 m) a 9.81 m = 16.0 s s 2 66. ANS: F = F y 2 + F x 2 = (6.0 N) 2 + (4.0 N) 2 = 7.2 N 67. ANS: weight = F g = m a = 0.9 kg ( 9.81 m s 2) 1 = 1.47 kg 1 kg 6 68. ANS: v y = v sin θ = 2.50 m s (sin 40.0) = 1.61 m s 69. ANS: assuming no air resistance, v x = v xo, v y = a y t + v 0 and v = v y 2 + v x 2 therefore, v = v y 2 + v x 2 = (a y t + v 0 ) 2 + (v xo ) 2 = ( 9.81 m s 2 (4 s) + 30 m s )2 + (10 m s )2 = 13.6 m s θ = tan 1 v y v x = tan m ( 9.81 1 s 2(4 s)+30 m s ) 10 m s = 42.7 or 317.3 70. ANS: range = (v 0 2 )sin 2θ = (755 m s )2 sin 2(38.5 ) a y 9.81 m = 56 600 m s 2 71. ANS: y max = v 0 2 sin 2 θ + y 2a 0 v 0 = 2a y (y max y 0 ) y sin 2 θ = 2( 9.81m s2)(25.0 m) = 31.3 m sin 2 45.0 s
72. ANS: Free body diagram shows F g vector pointing straight down from the center of the trapeze and F N vector pointing straight up from the same point. F ga and F gb vectors point straight down from each end of the trapeze, and F TA and F TB vectors point straight up from the same points at each end of the trapeze. F g = m g = 45.5 kg ( 9.81 m s2) = 446 N F F ga = F gb = m g 2 N = F g = ( 446 N) = 446 N m (45.5 kg +1.00 kg) ( 9.81 s = 2) = 228 N F 2 TA = F TB = F ga = ( 228 N) = 228 N F TA F N F TB F GA F g F gb 73. ANS: Free body diagram shows force of gravity vector pointing down and force of friction vector pointing straight up. Both vectors originate at the skydiver/parachute center of gravity. At terminal velocity a = 0, F net = F g + F f and F net = m a therefore, F net = (55.5 kg + 12.5 kg) (0 m s 2) = 0 = F g + F f F f = F g F g = m g = (55.5 kg + 12.5 kg) ( 9.81 m s 2) = 666 kg and F f = ( 666 kg) = 666 kg F f F g 74. ANS: F net = m a and F net = F p + F f therefore, m a = F p + F f a = F p+f f m 300 N+( 100 N) = = 4 m 50 kg s 2 75. ANS: There is no friction nor is any person or mechanical device pushing the box. Therefore, gravity is the only force causing the crate to move down the box, so we need to rotate the axes and find the component force of gravity that is parallel with the ramp. We will call this the x-component. F net = m a and F net = F p + F f + F gx = 0 N + 0 N + F gx therefore, F gx = m a F gx = F g cos θ F g cos θ = m a a = F g cos θ m m 25.5 kg ( 9.81 s2) cos(270 30.0 ) = 25.0 kg = 4.91 m s 2