Alice bungee-jumps from a bridge above a deep gorge. Bob watches from the bridge. Let event $D$ be Alice's departure from Bob's location on the bridge, and event $R$ be her return to Bob's location on the bridge. Carol observes these events from a a train passing over the bridge, and uses synchronized clocks on the train to measure the time between Alice's departure and return.
-(c) Which person's watch or clocks register(s) a coordinate time between those events in some inertial frame?
A) Alice
B) Bob
C) Carol
D) Alice and Bob
E) Bob and Carol
F) Alice and Carol
G) All three observers

Question

Quizplus · Accepted Answer

Bob and Carol are in inertial frames relative to the events of Alice's departure and return, so their clocks can measure the coordinate time between these events. Alice, however, is in a non-inertial frame due to the acceleration involved in bungee jumping, making her perspective unsuitable for measuring coordinate time in an inertial frame.

Alice Bungee-Jumps from a Bridge Above a Deep Gorge DDD Be Alice's Departure from Bob's Location on the Bridge, and Watches

Alice Bungee-Jumps from a Bridge Above a Deep Gorge $D$ Be Alice's Departure from Bob's Location on the Bridge, and Watches