"fifteen hundred years ago everybody knew the earth was the center of the universe. five hundred years ago, everybody knew the earth was flat, and fifteen minutes ago, you knew that humans were alone on this planet. imagine what you’ll know tomorrow.” that's a statement of agent kay in from men in black. agent kay's statement illustrates that theories are a) always true. b) constantly changing. c) describe what happens in the natural world. d) are proven by evidence collected by scientists.

As you are trying to move a heavy box of mass m, you realize that it is too heavy for you to lift by yourself. there is no one around to , so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. you pull up on the rope to lift the box. use g for the magnitude of the acceleration due to gravity and neglect friction forces. once you have pulled hard enough to start the box moving upward, what is the magnitude f of the upward force you must apply to the rope to start raising the box with constant velocity? express the magnitude of the force in terms of m, the mass of the box.

Acoil suspended freely, points in some direction when no current is passed through it . can you tell what will happen when a current is passed though it?

Name two kinds of practical electric pumps.