You lift a 6.5-kg backpack from a chair that is 0.47 m above the floor (hc) to a desk that is 0.75 m above the floor (hd). a. When the backpack is on the desk, what is the backpack-Earth system’s gravitational potential energy relative to the floor (GPE1)?
b. When the backpack is on the desk, what is the backpack-Earth system’s gravitational potential energy relative to the chair (GPE2)?
c. How much work was done by gravity as you lifted the backpack from the chair to the desk?