Dave visiting an amusement park spots a mechanical bull ride. Dave watches several customers ride the mechanical bull, and he decides it looks like fun. He pays a fee to ride the mechanical bull. The attendant at the ride gives Dave a piece of paper to sign prior to riding the mechanical bull. The paper says, "I understand that riding this mechanical bull is a dangerous activity with the risk of serious injury." Dave signs the paper, hops up on the mechanical bull, is thrown onto the surrounding mat, and suffers a compound fracture to his leg. Is the amusement park liable in tort to Dave? Why or why not?