20. A semiconductor is a crystalline solid that conducts current under any condition
metallic solid that conducts current under any condition
metallic solid that conducts current under certain conditions
crystalline solid that conducts current under certain conditions

If the work required to stretch a spring 3 ft beyond its natural length is 15 ft-lb, how much work is needed to stretch it 27 in. beyond its natural length?

Which describes increasing the efficiency of energy resource

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.