"A high-speed train is traveling at a constant $150$ m/s (about $300$ mph) on a straight horizontal track across the south pole. Find the angle between a plumb line suspended from the ceiling inside the train and another inside a hut on the ground. In what direction is the plumb line on the train deflected?"

we're looking for is a relationship $\mathrm{tan}(\theta )=\frac{{a}_{n}}{{a}_{t}}$, because for the plumb line in the hut ${a}_{t}=1$ but not for the plumb line in the train due to the Coriolis force.

However,

1. What is the frame of reference here? Is it rotating, fixed so that the train is standing still? Is it rotating with the earth?

2. Since the train is on the south pole, isn't that the same to say that the earth's rotation doesn't affect it?

3. Can you show me how to get the right answer? The right answer is supposed to be $0.13$ degrees. In which direction?

we're looking for is a relationship $\mathrm{tan}(\theta )=\frac{{a}_{n}}{{a}_{t}}$, because for the plumb line in the hut ${a}_{t}=1$ but not for the plumb line in the train due to the Coriolis force.

However,

1. What is the frame of reference here? Is it rotating, fixed so that the train is standing still? Is it rotating with the earth?

2. Since the train is on the south pole, isn't that the same to say that the earth's rotation doesn't affect it?

3. Can you show me how to get the right answer? The right answer is supposed to be $0.13$ degrees. In which direction?