Bernard wacks a 0.058-kg tennis ball at rest. He exerts a force of 12 newtons of a 0.1 second time interval. What is the final speed of the tennis ball

wavelength divides in half and speed stays the same.

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.