UNIT 4: FORCES IN NATURE Test review: 4_1_ Forces in nature. Fundamentals

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1 UNIT 4: FORCES IN NATURE Test review: 4_1_ Forces in nature. Fundamentals 1. Contact forces are examples of which of the fundamental forces? a. Strong c. Weak b. Electromagnetic d. Gravitational 2. The nucleus of a helium atom is an alpha particle, which consists of two protons and two neutrons. Which statement best explains how the two protons in an alpha particle can be bound so closely together? a. The strong nuclear force and the electromagnetic force are the same. b. The strong nuclear force and the electromagnetic force are negligible. c. The strong nuclear force is weaker than the electromagnetic force. d. The strong nuclear force is stronger than the electromagnetic force. 3. The strong force is the force of a. repulsion between protons. c. repulsion between nucleons b. attraction between protons and d. attraction between nucleons electrons 4. The diagram below shows a worker using a rope to pull a cart. The worker s pull on the handle of the cart can best be described as a force having a. magnitude, only c. both magnitude and direction b. direction, only d. neither magnitude nor direction

2 SUPERPOSITION OF FORCES 5. A 10-newton force and a 15-newton force are acting from a single point in opposite directions. What additional force must be added to produce equilibrium? a. 5 N acting in the same direction as the 10-N force b. 5 N acting in the same direction as the 15-N force c. 10 N acting in the same direction as the 10-N force d. 25 N acting in the same direction as the 15-N force 6. The vector diagram below represents two forces, F1 and F2, simultaneously acting on an object. Which vector best represents the resultant of the two forces? 7. Four tugs apply forces to an oil-rig in the directions shown. Which of the following could represent the direction of the resultant force? 8. Which pair of forces acting concurrently on an object will produce the resultant of greatest magnitude? a. 1 c. 3 b. 2 d. 4 e. The resultant is the same for all the pair of forces 9. Forces A and B have a resultant R. Force A and resultant R are represented in the diagram below.

3 Which vector best represents force B? 10. Two 30.-newton forces act concurrently on an object. In which diagram would the forces produce a resultant with a magnitude of 30. newtons? NEWTON S LAWS OF MOTION. FIRST LAW. LAW OF INERTIA A lab cart is loaded with different masses and moved at various velocities. Which diagram shows the cartmass system with the greatest inertia? If the sum of all the forces acting on a moving object is zero, the object will a. slow down and stop c. continue moving with constant velocity b. change the direction of its motion d. accelerate uniformly 13. Which person has the greatest inertia? a. a 110-kg wrestler resting on a mat c. a 70-kg long-distance runner traveling at 5 m/s b. a 90-kg man walking at 2 m/s d. a 50-kg girl sprinting at 10 m/s e. All have the same inertia 14. Which object has the most inertia? a. a kilogram bumblebee traveling at 2 meters per second b. a 0.1-kilogram baseball traveling at 20 meters per second c. a 5-kilogram bowling ball traveling at 3 meters per second d. a 10.-kilogram sled at rest e. All have the same inertia 15. The picture shows the circular path of a toy plane being swung around on a string. What path would the toy take if the string broke?

4 16. Based on the diagram below, which shows a 1.0-newton metal disk resting on an index card that is balanced on top of a glass. What is the net force acting on the disk? a. 1.0 N c. 0 N b. 2.0 N d. 9.8 N e. It depends on the mass of the disk 17. When the index card above is quickly pulled away from the glass in a horizontal direction, the disk falls straight down into the glass. This action is a result of the disk s a. inertia c. shape b. charge d. temperature e. color 18. A spacecraft completes the last stage of its journey back to Earth by parachute, falling with constant speed into the sea. The spacecraft falls with constant speed because a. the gravitational field strength of the Earth is constant near the Earth s surface c. the air resistance is greater than the weight of the spacecraft b. it has come from space where the gravitational field strength is almost zero d. the weight of the spacecraft is greater than the air resistance e. the air resistance is equal to the weight of the spacecraft NEWTON S LAWS OF MOTION. SECOND LAW. F= ma 19. A 50-kg child on a skateboard experiences a 75-N force as shown. What is the expected acceleration of the child? a m/s 2 c m/s 2 b m /s 2 d m/s Which one of the following quantities can have its unit expressed as kg m s -2? a. Force c. Energy

5 b. Power d. Pressure 21. The figure shows a block that is being pulled along the floor. According to the figure, what is the acceleration of the block? a. 2 m/s 2 c. 4 m/s 2 b. 3 m/s 2 d. 5 m/s 2 e. 6 m/s The diagram shows the horizontal forces acting on a box. The box accelerates at 1.6 m/s 2. The mass of the box is a kg c kg b kg d kg e kg. 23. Five cars are acted on by different forces. Which car is speeding up to the right? 24. A net force of 10. newtons accelerates an object at 5.0 m/s 2. What net force would be required to accelerate the same object at 1.0 m/s 2?

6 a. 1.0 N c. 2.0 N b. 5.0 N d. 50. N An object of 5.00 kg mass moves only to the right along the +x-axis. During some time interval, the object s speed is increased from 4.00 m/s to 8.00 m/s with a constant acceleration of 2.00m/s 2.. What is the net force acting on the object during the time interval of the acceleration? a N c N b N d N e. The answer cannot be determined without more information about the forces involved Which one of the following choices correctly identifies all of the listed situations for which there is a non-zero net force? Situation I : A point object moves in a straight line with increasing speed. Situation II : A point object moves in a circular path with constant speed. Situation III : A point objects moves in a circular path with decreasing speed.? a. Situations I, II, & III c. Only Situations II & III b. Only Situations I & III d. Only Situation III e. Only Situation I A communication satellite is in a circular orbit around Earth. If the speed of the satellite is constant, the force acting on the satellite a. is zero. c. is increasing. b. is decreasing. d. points toward the center of Earth at all times. e. points in the direction that the satellite is moving. An object moves to the East across a frictionless surface with constant speed. A person then applies a constant force to the North on the object. What is the resulting path that the object takes? a. A straight line path partly Eastward, partly Northward c. A parabolic path opening toward the North b. A straight line path totally to the North d. A parabolic path opening toward the East e. An exponential path opening upward toward the North 29. A 5.0 kg mass moves along the X-axis. At one instant of time, the mass has position 2.0 m, velocity 3.0 m/s, and acceleration 4.0 m/s 2. What is the net force acting on the mass at this instant of time? a. 0 N c N

7 b N d N e N 30. A box of mass 5.0 kg is being pushed to the right across a horizontal surface while a constant frictional force of 8.0 N acts on the box. At some instant of time, the box has a speed of 4.0 m/s and an acceleration of 3.0 m/s 2. What is the magnitude of the net force acting on the box at this instant? a. 7 N c N b N d N e N NEWTON S LAWS OF MOTION. THIRD LAW. ACTION AND REACTION A soccer player kicks a 0.5-kilogram stationary ball with a force of 50 newtons. What is the force on the player s foot? a. 0 N c. 50 N b. 25 N d. 100 N e. 0.5 N Which of the following statements is most closely associated with Newton s Third Law of Motion? a. What goes up must come down. c. An object at rest remains at rest. b. For every action force, there is an equal but opposite reaction force. d. The acceleration of an object is directly proportional to the force acting on the object but inversely proportional to the mass of the object. e. The Universe tends toward disorder A person sits on a chair which rests on the Earth. The person exerts a downward force on the chair. Which of the following is the reaction to this force? a. The force of the chair on the person c. The force of the Earth on the person b. The force of the person on the chair d. The force of the chair on the Earth e. The force of the person on the Earth A student holds a book at rest in an outstretched hand. The force exerted on the book by the student is equal to the book s a. mass c. volume b. weight d. density A rocket is taking off from the surface of the Earth. The rocket engines exert a force on the exhaust gases. Which of the following is the reaction to this force? a. The force of the Earth on the exhaust c. The force of the rocket engines on the gases. Earth. b. The force of the Earth on the rocket d. The force of the exhaust gases on the

8 engines. Earth. e. The force of the exhaust gases on the rocket engines. 36. A spring scale reads 20. newtons as it pulls a 5.0-kilogram mass across a table. What is the magnitude of the force exerted by the mass on the spring scale? a. 49 N c. 5.0 N b. 20. N d. 4.0 N 37. A man is pushing a baby stroller. Compared to the magnitude of the force exerted on the stroller by the man, the magnitude of the force exerted on the man by the stroller is a. zero c. larger b. smaller, but greater than zero d. Sometimes smaller and sometimes larger, depending on the way the man is pushing the baby stroller e. the same 38. A physics book sits at rest on a table. On top of the book is a calculator, also at rest. Which one of the following choices is the Newton s Third Law pair force to the force that the table exerts on the book? a. The contact force on the table by the book b. The gravitational force on the book by the Earth. c. The gravitational force on the combination of the book and calculator by the Earth. d. The contact force on the book by the calculator. e. The contact force on the table by the ground supporting it. 39. A skydiver falls downward through the air with constant speed. Which one of the following choices correctly describes the Newton s Third Law pair force to the air resistance acting on the skydiver during the fall? a. There is no Third Law pair force for this kind of situation. b. The gravitational force acting on the skydiver by the Earth. c. The force that molecules in the air exert on neighboring molecules in the air d. The force exerted on molecules in the air by the ground. e. The force exerted on molecules in the

9 air by the skydiver. 40. A 400-newton girl standing on a dock exerts a force of 100 newtons on a newton sailboat as she pushes it away from the dock. How much force does the sailboat exert on the girl? a. 25 N c. 400 N b. 100 N d N e N

10 Test review: 4_1_ Forces in nature. Fundamentals. Key part If you have 35 correct answers you can feel confident. 1.b. 11.e. 21.a. 31.c. 2.a. 12.c. 22.b. 32.b. 3.d. 13.a. 23.a. 33.a. 4.c. 14.d. 24.c. 34.b. 5.a. 15.a. 25.a. 35.e. 6.b. 16.c. 26.a. 36.b. 7.e. 17.a. 27.d. 37.e. 8.d. 18.e. 28.c. 38.c. 9.b. 19.b. 29.d. 39.e. 10.c. 20.a. 30.c. 40.b.