The Pendulum and Truck Puzzle
December 2nd, 2007
| Categories: Mechanics, Physics Puzzles
Still working on the next part of our neural networks tutorial, but in the meantime, a puzzle.
A stationary truck has a pendulum of length L and mass m attached to the top of its insides (see figure A below). The truck driver hits the acceleration and as a result everything sort of gets “thrown back” inside the track - pendulum included (see figure B below). The question is, can the calculate the maximal angle the pendulum reaches as it is thrown back? Neglect air friction, or any other type of friction in this problem.
Enjoy!
Is the acceleration constant? If it is, one can use the equivalence principle to say the effective gravitational force is now m (vec{g} - vec{a}) in the accelerating frame of the truck. So theta is ArcTan|a/g|.
I said MAXIMAL angle, not the angle at equilibrium :). But you are on the right track!
It must be 2 ArcTan|a/g| by the conservation of energy.