chapter 4

# chapter 4 - Chapter 4 The Laws of Motion Quick Quizzes 1(a...

This preview shows pages 1–3. Sign up to view the full content.

Chapter 4 The Laws of Motion Quick Quizzes 1. (a) True. Motion requires no force. Newton’s first law says an object in motion continues to move by itself in the absence of external forces. (b) False. It is possible for forces to act on an object with no resulting motion if the forces are balanced. 2. (a) True. If a single force acts on an object, it must accelerate. From Newton's second law, = m Σ aF G G , and a single force must represent a non-zero net force. (b) True. If an object accelerates, at least one force must act on it. (c) False. If an object has no acceleration, you cannot conclude that no forces act on it. In this case, you can only say that the net force on the object is zero. 3. False. If the object begins at rest or is moving with a velocity with only an x component, the net force in the x direction causes the object to move in the x direction. In any other case, however, the motion of the object involves velocity components in directions other than x . Thus, the direction of the velocity vector is not generally along the x axis. What we can say with confidence is that a net force in the x direction causes the object to accelerate in the x direction. 4. (a). Because the value of g is smaller on the Moon than on the Earth, more mass of gold would be required to represent 1 newton of weight on the Moon. Thus, your friend on the Moon is richer, by about a factor of 6! 5. (c) and (d). Newton’s third law states that the car and truck will experience equal magnitude (but oppositely directed) forces. Newton’s second law states that acceleration is inversely proportional to mass when the force is constant. Thus, the lower mass vehicle (the car) will experience the greater acceleration. 6. (c). The scale is in equilibrium in both situations, so it experiences a net force of zero. Because each person pulls with a force F and there is no acceleration, each person is in equilibrium. Therefore, the tension in the ropes must be equal to F . In case (i), the person on the right pulls with force F on a spring mounted rigidly to a brick wall. The resulting tension F in the rope causes the scale to read a force F . In case (ii), the person on the left can be modeled as simply holding the rope tightly while the person on the right pulls. Thus, the person on the left is doing the same thing that the wall does in case (i). The resulting scale reading is the same whether there is a wall or a person holding the left side of the scale. 99

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
100 CHA P T E R 4 7. (c). The tension in the rope has a vertical component that supports part of the total weight of the child and sled. Thus, the upward normal force exerted by the ground is less than the total weight. 8. (b). Friction forces are always parallel to the surfaces in contact, which, in this case, are the wall and the cover of the book. This tells us that the friction force is either upward or downward. Because the tendency of the book is to fall due to gravity, the friction force must be in the upward direction.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 44

chapter 4 - Chapter 4 The Laws of Motion Quick Quizzes 1(a...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online