If there is no slipping, a frictional force must exist between the wheels and the ground. in what direction does the frictional force from the ground on the wheels act? take the positive x direction to be to the right.

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