Two cars approach each other; both cars are moving westward, one at 71 km/h, the other at 67 km/h. what is the magnitude of the velocity of the first car relative to (in the frame of reference of) the second car? answer in units of km/h.

Which of the following best describes internal energy? a. the difference between the kinetic and potential energies of the particles in a system b. the sum of the kinetic and potential energies of the particles in a system c. the sum of the kinetic and thermal energies of the particles in a system d. the difference between the kinetic and thermal energies of the particles in a system