P18: A nonlinear spring model could include a cubic term. That is, the force is approximated by F(x) = –kx + k’x3 . a) If all quantities are in our usual (SI) units, what are the units of k and k’? b) For a particular spring, the constants are k = 300 and k’ = 5x104 . How much does the potential energy in the spring change when it is stretched from x = 0.02 m to 0.05 m?

Atennis player used a tennis racket to hit a tennis ball with a mass of 0.25 kg with a force of 5.25 newtons. how does the force the tennis racket exerted on the tennis ball compare with the force the tennis ball exerted on the tennis racket? a. the force of the tennis racket on the tennis ball is equal in magnitude and opposite in direction to the force the tennis ball exerted on the tennis racket. b. the force of the tennis racket on the tennis ball is equal in magnitude and in the same direction as the force the tennis ball exerted on the tennis racket. c. the force of the tennis racket on the tennis ball is less in magnitude and in the same direction as the force the tennis ball exerted on the tennis racket. d. the force of the tennis racket on the tennis ball is greater in magnitude and opposite in direction as the force the tennis ball exerted on the tennis racket.