You are performing studies of the possibility of migrating birds using the earth's magnetic field for navigation. to modify the magnetic field in the brain of a bird, you fit the bird with coils as "caps" and "collars"

the data on the coils indicate that they each have 210 q of resistance, a radius of 1.20 cm, and 50 turns of wire. the centers of the coils are separated by 2.05 cm. you wish to create an "earth-like" magnetic field of 4.0 x 105 t at the midpoint of the axis between the coils. given this data, you need to determine the voltage of the battery (in v) needed to power the coils

v=

In an old-fashioned amusement park ride, passengers stand inside a 3.0-m-tall, 5.0-m-diameter hollow steel cylinder with their backs against the wall. the cylinder begins to rotate about a vertical axis. then the floor on which the passengers are standing suddenly drops away! if all goes well, the passengers will “stick” to the wall and not slide. clothing has a static coefficient of friction against steel in the range 0.60 to 1.0 and a kinetic coefficient in the range 0.40 to 0.70. part a what is the minimum rotational frequency, in rpm, for which the ride is safe? express your answer using two significant figures. f f = rpm