Does the tank fall into the trap?
There is no such thing as a rigid body in relativity (or else
signals could be sent faster than light). What happens is that the front
end of the tank sags a little bit as it comes to the hole. I exagerated the
pictures of course: Actually, if the tank is going fast enough, the effect of
gravity would cause it to fall very slightly; that is, its fall (right picture)
would be just the amount of sag (left picture).
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