4. (2 pt) In an amusement park ride people are "flying" in a circle. Which statement is true? (a) Centrifugal force is pulling the people away from the center of the circle. (b) The chair a person sit on is pushing him toward the center of the circle. (c) Both of the above. (d) Neither of the above. 5. (2 pt) In a rotating vertical cylinder (Rotor-ride) a rider finds herself pressed with her back to the rotating wall. Which is the correct free-body diagram for her? (a) (b) (c) (d) (e) Problems The following problems will be graded. For full credit, please show your work, including diagrams, algebraic equations, and enough written explanations that somebody who is not familiar with the problem could understand what you are doing. A final numerical answer is only one small part of a complete solution; an answer with no work shown will not be given any credit. 6. (5 pt) Again, consider the off-road vehicle shown in the picture. If the hill and the valley have a radius of curvature R=80m, how fast can the car go without losing contact with the road (i.e., getting "airborne") at the top of the hill