26. An observer in frame S observes a photon travelling in a direction making 60 with the X-axis. A frame S' travels with a speed 0.6 c along the common X- X' axis. What angle does the photon make with the X'-axis as observed by an observer in S'? (Ans. 81.8 above the negative X'-axis) Hint: U, = 0.500c, U, 0.866c. Find U,U and tan 0' = U 27. A space traveller on a rocket notes that he is travelling towards a star 1 light year away from the earth with a speed v. An observer on earth finds that the rocket is travelling with a speed v but says the star is 10 light years away. (a) How long does the trip last according to the space traveller? (b) How long does the trip last according to the observer on the earth? Who is correct? (Ans. (a) 1.0005 y (b) 10.05 y. Both are correct) her baby says 28. Assume that the speed of light is 100 km/h. A lady relating the story of the delivery she drove herself at 80 km/h to the hospital which was 100 km away as per the highway board. She also claims that according to her watch the baby was born 1 hour after she left. Show that the baby was born in the hospital.