10. 11. Homework 4 How many forces are required for an interaction? To produce a net force on a system, must there be an externally applied net force? Earth pulls down on you with a gravitational force that you call your weight. Do you pull Up on Earth with the same amount of force? How does a helicopter get its lifting force? what happens to the magnitude of the normalvector on a block resting on an incline when the angle of the incline increases? How does the magnitude of the vertical component of velocity for a ball tossed at an upward angle change as the hall travels upward? How about the horizontal component of velocity when air resistance is negligible? For each of the following interactions. identify action and reaction forces: [a1 A hammer hits a nail. 1b} Earth gravity pulls down on a book. to] A helicopter blade pushes air downward. Consider the two forces acting on the person who stands stillnamely, the downward pull of gravity and the upward support of the oor. Are these forces equal and opposite? Do they form an action reaction pair? Why or why not? .1 d Suppose that Mocarls. one twice as massive as the other, y apart when the compressed spring that joins them is released. What is the acceleration of the heavier cart relative to that of the lighter cart as they start to move apart? It a Mack truck and Honda Civic have a head-on collision. upon which vehicle is the impact force greater? which vehicle experiences the greater deceleration? Explain your answers. Consider a ball rolling around in a circular path on the inner surface of a cone [see the gure below]. The weight of the hall is shown by the vector W. Iwithout friction, only one other force acts on the halla normal force. {a} Draw in the vector for the normal force. {The length ofthe vector depends on the next step, b.) [b] Using the parallelogram rule, show that the resultant of the two vectors is along the radial direction of the ball's circular path. ltires, the normal is appreciably greater than the weight!)- 12. Suppose you roll a ball off a tabletop. will the time to hit the oor depend on the speed ofthe ball? [will a fast ball take a longer time to hit the floor?) Defend your