Alice is driving a race car around an essentially circulartrack.  Brian, who is sitting at a fixed position at theedge of the track, measures the time that Alice takes to complete alap by starting his watch when Alice passes by his position (callthis event E) and stopping it when Alice passes his positin again(call this event F).  This situation is also observed byCara and Dave, who are passengers in a train that passes very closeto Brian.  Cara happens to be passing Brian just as Alicepasses Brian for the first time, and Dave happens to pass Brianjust as Alice passes Brian the second time.  Assume thatthe clocks used by Alice, Brian, and Cara are close enough togetherso that we can consider them all to be \"present\" at event E, andsimilarily that those used by Alice, Brian, and Dave are \"present\"at event F.  Assume that the ground frame is an inertialreference frame.
Who measures:
a) the proper time,
b) the coordinate time,
c) and the spacetime interval between events E and F?
Explain why.
