I read the section on thermal/mechanical/potential/kinetic energy in my physics book and i seriously have NO idea how to apply what i learned in these problems. I am so confused, i never been this confused before in phsyics. I am getting very frustrated..man physics is so frustrating!!! 5) The temp. of a plastic cube is monitored while the cube is pushed 3.5 m across a floor at constant speed by a horizontal force of 15 N. The monitoring reveals that the thermal energy of the cube increases by 20 J. What is the increase in the thermal energy of the floor along which the cube slides? 6) A 41 g bullet with horizontal velocity of 496 m/s stops 13 cm within a solid wall. What is the change in mechanical energy 7) 5.8e6 kg of water fall 50 m over Niagara Falls each second. What is the decrease in gravitational potential energy of the water-Earth System.