Rock x is released from rest at the top of a cliff that is on earth. a short time later, rock y is released from rest from the same location as rock x. both rocks fall for several seconds before landing on the ground directly below the cliff. frictional forces are considered to be negligible. which of the following graphs correctly shows the vertical velocity of rock x as a function of time? take the positive direction to be upward.

Electric field of the earth. the earth has a net electric charge that causes a field at points near its surface equal to 150 n> c and directed in toward the center of the earth. (a) what magnitude and sign of charge would a 60-kg human have to acquire to overcome his or her weight by the force exerted by the earth’s electric field? (b) what would be the force of repulsion between two people each with the charge calculated in part (a) and separated by a distance of 100 m? is use of the earth’s electric field a feasible means of flight? why or why not?