Notice that a ball dropped from rest eventually reaches a constant speed called the terminal speed.  This is equal to g/k where g is the acceleration due to gravity and k is a constant that is proportional to the force of air resistance at a certain speed.  You can set a value of k before clicking on a link in order to observe its effect on the motion of the projectile.

Answer the following questions:

1.  Suppose a skydiver is falling at her terminal speed when she pulls her 'chute.  During the time interval that the chute opens, what direction is her acceleration?

2.  If a projectile is projected downward with an initial speed greater than g/k, the object's terminal speed, is its instantaneous acceleration, at any instant before it reaches terminal speed, positive or negative?

 

Position vs. Time Velocity vs. Time Acceleration vs. Time