A train is moving down the tracks at 18m/s. The conductor sees a stalled train on the tracks ahead and slams on the breaks. The breaking train has an acceleration of -6m/s/s. How far does the train go before it stops?

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.