10. A rocket is moving at such a speed that its length as measured by an observer on the earth is only half of its proper length. How fast is the rocket moving relative to the earth? 11. How fast must a space ship travel if a traveller in the space ship ages at only half the rate we are ageing on the earth? 12. An air plane is moving with respect to earth with a speed of 600 m/s. As determined by earth clock, how long will it take for the air plane clock to fall behind by a microsecond? (Ans. 0.866 c) (Ans. 0.866 c) (Ans. 5 x 10 s = 5.8 days approx.) At Plane - 2 x 1012 Atearth = At plane 106 Hint: Atearth = , l arth 1/2 1-