On Planet X, a ball on a massless, rigid rod oscillates as a simple pendulum with a period of 2.0s. If the pendulum is taken to the moon of Planet X, where the free-fall acceleration g is half as big, the period will be

a.2.8 s
b.4.0 s
c.2.0 s
d.1.4 s
e.1.0 s

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.)