A bob is suspended on a string inside a boxcar?

Question

The boxcar moves without friction down the slope
on track inclined 2 degrees to horizon.

What is inclination of the string to the vertical?

Answer 1

Once a steady speed is reached, 88 degrees, 2 degrees less than the 90 degree angle that the string would normally have with the roof

Answer 2

Without computing, I'm going to guess it hangs straight down due to some sort of relativity principle.

Okay, fine, I'll compute:

Assuming no engine power, no friction, nothing but gravity: acceleration on the car is g sin theta forward, so there's a psuedoforce on the bob:
g sin theta backwards

acceleration due to gravity on the bob:

g cos theta down
g sin theta forward

So the gravity and the pseudoforce cancel in the front/back direction, and the only thing the bob notices is that it is slightly lighter than normal. So it hangs straight down as I (and Mr. Flibbity) guessed.

Answer 3

If you were in the box with the bob, it would appear perpendicular to the ceiling.
That means the string and the ceiling make a right angle.

Answer 4

What did poor Bob do to deserve that?