A45.0-kg girl is standing on a 166-kg plank. the plank, originally at rest, is free to slide on a frozen lake, which is a flat, frictionless surface. the girl begins to walk along the plank at a constant velocity of 1.48 m/s to the right relative to the plank. (let the direction the girl is moving in be positive. indicate the direction with the sign of your answer.)
1. what is her velocity relative to the surface of the ice?
2. what is the velocity of the plank relative to the surface of ice?

Certain bacteria (such as aquaspirillum magnetotacticum) tend to swim toward the earth’s geographic north pole because they contain tiny particles, called magnetosomes, that are sensitive to a magnetic field. if a transmission line carrying 100 a is laid underwater, at what range of distances would the magnetic field from this line be great enough to interfere with the migration of these bacteria? (assume that a field less than 5% of the earth’s field would have little effect on the bacteria. take the earth’s field to be 5.0 * 10-5 t, and ignore the effects of the seawater.)