(2-5)   Look at the picture below: you are in the exact centre of a fast-moving railway carriage, armed with a flashlight. Equidistant from you are, at the front end of the carriage, Vlad the Impaler (V) and at the back end, Margaret Thatcher (M). It is dark. Nefertiti (N), meanwhile, is waiting on the station platform. From her point of view (on the left in the picture), the train is coming from the left and moving towards the right. On the other hand, in your frame of reference (on the right below), the carriage is stationary, with you in the middle, while Nefertiti passes by, heading to the left.

At the exact moment when you and Nefertiti draw level, you flash your light: