Question 19N.3.SL.TZ0.c(iii)
| Date | November 2019 | Marks available | [Maximum mark: 2] | Reference code | 19N.3.SL.TZ0.c(iii) |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Demonstrate | Question number | c(iii) | Adapted from | N/A |
A train is moving across a bridge with a speed v = 0.40c. Observer A is at rest in the train. Observer B is at rest with respect to the bridge.
The length of the bridge LB according to observer B is 2.0 km.
According to observer B, two lamps at opposite ends of the bridge are turned on simultaneously as observer A crosses the bridge. Event X is the lamp at one end of the bridge turning on. Event Y is the lamp at the other end of the bridge turning on.
Events X and Y are shown on the spacetime diagram. The space and time axes of the reference frame for observer B are and ct. The line labelled ct' is the worldline of observer A.
Demonstrate, using the diagram, which lamp observer A observes to light first.
[2]
light worldlines at 45° from X AND Y intersecting the worldline ct′ ✔
so light from lamp X is observed first ✔
NOTE: Allow lines drawn without a ruler.
Do not allow MP2 without supporting argument or correct diagram.
