Pick the right statement about normal force: (section 5.7)
a. normal force is always perpendicular to the area of contact between an object and support
b. normal force is always antiparallel and equal in magnitude to force of gravity (weight).
c. normal force is always equal in magnitude to force of gravity (weight).
d. normal force is always antiparallel to force of gravity (weight), meanwhile its magnitude can be any.

Askydiver weighing 140 lb (including equipment) falls vertically downward from an altitude of 19,000 ft and opens the parachute after 18 s of free fall. assume that the force of air resistance, which is directed opposite to the velocity, is of magnitude 0.55|v| when the parachute is closed and is of magnitude 14|v| when the parachute is open, where the velocity v is measured in ft/s. assume that acceleration due to gravity has magnitude 32 ft/s/s; remember that weight is the product of mass and gravitational acceleration. (a) find the speed of the skydiver when the parachute opens. (b) find the distance fallen before the parachute opens. (c) what is the limiting velocity vl after the parachute opens? (d) determine how long the sky diver is in the air after the parachute opens. (e) plot the graph of velocity versus time from the beginning of the fall until the skydiver reaches the ground.

Suppose you increase your walking speed from 7 m/s to 13 m/s in a period of 2 s. what is your acceleration?

Which type of basaltic lava flow has a fairly smooth