If you make an electromagnet using a battery circuit and a steel nail, how can you increase its magnetic strength?

a.
replace the nail with a copper rod

b.
wrap more coils of wire around the nail

c.
use a longer nail

d.
remove the plastic insulation from the wire coil

Abumper car with a mass of 250 kg is traveling at a speed of 4 m/s. this bumper car collides and sticks to a second bumper car with a mass of 250 kg, which is initially at rest. what is the final speed of these two bumper cars after the collision, assuming they remain stuck together?