A building contractor needs 500 sheets of drywall. Which is the most cost-effective way to buy them? 50 sheets at a time for $600 100 sheets at a time for $800 250 sheets at a time for $2,500 500 sheets at a time for $4,500

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