A long cable carries current I into the page (−ẑdirection) uniformly distributed over its circular cross- section of radius R. The same current I returns in the opposite direction (ẑdirection) along the surface of the cable (there is a very thin insulating layer separating the two currents). (a) What is the magnetic field B induced everywhere? (b) What is the energy stored in the cable per unit length? (c) What is the self-inductance L of the system per unit length? Hint: Use your answer from (b).

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.