A weightlifter is trying to carry a 10 kg weight held over his head across the room. How much energy will be required to do this work on the 10 kg weight?
No energy will be required, as no work is being done one the weight as it is carried across the room.
Wnc = Fdcos90
cos90 = 0
Wnc = 0
Wnc = change in Emech
change in Emech = 0