Heat energy is:

a. the internal motion of atoms
b. stored in the bonds of atoms
c. stored in the nucleus of atoms
d. moving electrons

all and any is appreciated

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?