You are outside a store, moving a loaded grocery cart down the street on a very steep hill. It is difficult, but you are able to pull back on the handle and keep the cart moving down the street in a straight line and at a constant speed. For this situation, the forces on the cart are.
a. unbalanced, in the direction of the movement
b. balanced, with a net force of zero.
c. equal to the force of gracty acting on the cart.
d. greater than the frictional forces opposing the motion of the cart.