What does an unconformity in a sequence of rock layers reveal about geologic history?
a.
a rock layer must have turned upside down.
b.
a layer of rock might have eroded.
c.
the layers must cover hundreds of square miles.
d.
the layers must have been deposited very quickly.

The air that we breath is made mostly of which gaseous molecule

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.

The electric field direction is defined by the direction of the force felt by (select one of the following answers): 1. a negative charge. 2. a positive charge. 3. both positive and negative charges.