What is the si unit used to express gravitational potential energy?
a. newton
b. kilowatt
c. horsepower
d. joule

The SI unit used to express gravitational potential energy is Joule.

The answer is that they are composed mostly of liquid water.

I'm having some difficulty seeing the diagram clearly.but the question says there's a net inward force on the object.so we know right away,  from newton's 2nd law of motion, thatthat baby is accelerating.  it doesn't even matter which way thenet force is pointing.  if there's any net force, then either theobject's speed or else its direction must be changing.