Julia pushes her sled up a hill. In which direction is the force of friction

acting?

The force of friction acts down the hill.

Explanation:

Friction is a type of force that always act only when there is relative motion of an object.

Friction always opposes the motion of the change in state of the body and always acts in the direction opposite to the direction of motion. If the object is at rest and no force is acting on it, there will no frictional force acting on it.

If the object is in motion, it will act in the opposite direction.

Here, Julia pushes her sled up a hill. So, the motion of the sled is up the hill. So, frictional force will act in the opposite direction (down the hill) to oppose the motion.