17. A spaceship is moving with a large velocity past observer A, who is standing on Earth. Observer B is aboard the spaceship. Which of these observers measures the longer length for the length of the spaceship? Explain.

19. Is it possible for an astronaut to leave on a space trip and to return a year before her twin sister was born? Explain.

21. Could we use the relativistic momentum expression p =rmv, for objects moving at small velocities? Explain.

23. Is the increase in kinetic energy of an object equal to the work done to accelerate the object for an object moving at a very high speed? Explain.

25. f the velocity of an object is reduced to zero, does all of its energy disappear? Explain.

27. When you are inside a closed space vehicle, is it possible for you to tell whether the vehicle is accelerating or whether you are simply near some massive body such as the sun or the Earth? Explain.

29. Does light traveling in empty space always travel in a straight line? Explain.

31. Is a black hole just a hole in space that contains no mass? Explain.