You can find electric power lines under the ground by looking for magnetic fields at ground level. this is best explained by which of these statements?
a) all wires have magnetic materials in them.
b) an electric current in a wire produces a magnetic field.
c) the power company puts magnets to find the power lines.
d) the iron in the ground is disturbed by the power lines creating magnetic fields.

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.