| Date | May 2016 | Marks available | 4 | Reference code | 16M.3.SL.TZ0.6 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 0 |
| Command term | Deduce | Question number | 6 | Adapted from | N/A |
Question
An observer on Earth watches a rocket A. The spacetime diagram shows part of the motion of A in the reference frame of the Earth observer. Three flashing light beacons, X, Y and Z, are used to guide rocket A. The flash events are shown on the spacetime diagram.
The diagram shows the axes for the reference frames of Earth and of rocket A. The Earth observer is at the origin.
For the reference frame of the Earth observer, calculate the speed of rocket A in terms of the speed of light c.
Using the graph opposite, deduce the order in which
(i) the beacons flash in the reference frame of rocket A.
(ii) the Earth observer sees the beacons flash.
Markscheme
Δct=2.0km AND Δx=0.8km
\(v = \ll \frac{{\Delta x}}{{\Delta ct}} = \frac{{0.8}}{{2.0}} = \gg 0.4c\)
Allow any correct read-off from graph.
Accept answers from 0.37c to 0.43c.
(i) events at same perpendicular distance from x′ axis of rocket are simultaneous OR line joining X to Y is parallel to x′ axis
X and Y simultaneously then Z
MP1 may be present on spacetime diagram.
(ii) constructs light cones to intersect worldline of observer
X first followed by Y and Z simultaneously
Only Y and Z light cones need to be seen.
