An alien spacecraft is flying overhead at a great distance as you stand in your backyard. You see its searchlight blink on for 0.150 s. The first officer on the spacecraft measures that the searchlight is on for 12.0 ms. (a) Which of these two measured times is the proper time? (b) What is the speed of the spacecraft relative to the earth, expressed as a fraction of the speed of light c?

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.