7 Is this frame inertial? You\'re getting a video feed on your phone from a came

Question

7 Is this frame inertial? You're getting a video feed on your phone from a camera inside a railway boxcar that has no windows. You have no idea where this boxcar is or how the camera is oriented inside it, but you know that the camera is affixed to the frame of the car, ie. it's not moving relative to the car's interior. On your video screen, you see the following. The floor and ceiling look horizontal to you, i.e. you don't need to tilt your phone to some weird angle to have the floor in the image be parallel to the floor you're physically standing on. Hanging from the ceiling is a mass on a thin taut rope, only it's not hanging perpendicular to the boxcar floor in the video. Instead, it's hanging kind of down and left, making some noticeable angle with the ground, but the mass is otherwise stationary with respect to the boxcar interior.

Explanation / Answer

It is clear that

1. The mass is hanging from the ceiling making an angle with the ground.

2. The floor and ceiling inside the boxcar is parallel to that the observer is standing on.

3. The mass is stationary.

Thus it can be concluded that some pseudo force is acting on the mass and forcing it to make an angle with the ground. And this pseudo force arises from acceleration of the boxcar. Here the mass is stationary so a constant pseudo force is acting which arises from the constant acceleration of the boxcar. Since it is accelerating so the reference frame attached with the boxcar is non-inertial.

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