Homework 4

1. How many forces are required for an interaction?

1. To produce a net force on a system, must there be an externally applied net force?

1. 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?

1. How does a helicopter get its lifting force?

1. What happens to the magnitude of the normal vector on a block resting on an incline when the angle of the incline increases?

1. How does the magnitude of the vertical component of velocity for a ball tossed at an upward angle change as the ball travels upward? How about the horizontal component of velocity when air resistance is negligible?

1. For each of the following interactions, identify action and reaction forces: (a) A hammer hits a nail. (b) Earth gravity pulls down on a book. (c) A helicopter blade pushes air downward.

1. Consider the two forces acting on the person who stands stillnamely, the downward pull of gravity and the upward support of the floor. Are these forces equal and opposite? Do they form an action- reaction pair? Why or why not?