An object moving in a gravitational field is observed to speed up. Explain why.
A. The object has gained electrical potential energy.
B. The object is falling in the gravitational field, so it has gained kinetic energy.
C. The object has gained chemical potential energy.
D. The object is rising in the gravitational field, so it has lost kinetic energy.

At a certain instant after jumping from the airplane a, a skydiver b is in the position shown and has reached a terminal (constant) speed vb = 52 m/s. the airplane has the same constant speed va = 52 m/s, and after a period of level flight is just beginning to follow the circular path shown of radius ρa = 2330 m. (a) determine the velocity and acceleration of the airplane relative to the skydiver. (b) determine the time rate of change of the speed vr of the airplane and the radius of curvature ρr of its path, both as observed by the nonrotating skydiver.