Rita throws a ball straight up into the air and catches it at the
same position from which she threw it. the ball has 18 j of
mechanical energy when it leaves her hand.

when heated, the valance electrons increased their speed and transferred the heat from electron to electron.   i just took the test.

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.