A 42.2 kg sled is pulled forward with a 143 N force across
ground with k 0.269. What
is the net force on the sled?
(Unit = N)

the answer is b, have negligible mass

a skateboard rolling across the street - apex

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.