Aplane flies northwest out of o'hare airport in chicago at a
speed of 400 km/hr in a direction of 150 degrees (i. e., 30 degrees
north of west). the canadian border is located a distance of 1500
km due north of chicago. the plane will cross into canada after
approximately hours.

to treat tumors in the body

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.