Object a is stationary while objects b and c are in motion. forces from object a do 20 j of work on object b and -5 j of work on object c. forces from the environment do 4 j of work on object b and 8 j of work on object c. objects b and c do not interact. what are δktot and δu if (a) objects a, b, and c are defined as separate systems and (b) one system is defined to include objects a, b, and c and their interactions?