1. Marie pushes a box across the floor. What causes the box to move?

a. Mass

b. Marie's force

c. the force of friction

2. A basketball player is in the air during a jump shot. What directly exerted an external force on the player to accelerate him upward into the air?

a. his knees

b. the floor

c. the basket

d. his feet

3. A person in the figure is rolling a ball across the floor. Which force(s) indicated by arrows in the diagram need to be included in calculating the net force on the ball?

F T