One end of a thin rod is attached to a pivot, about which it can rotate without friction. Air resistance is absent. The rod has
a length of 0.35 m and is uniform. It is hanging vertically straight downward. The end of the rod nearest the floor is given a linear speed v0, so that the rod begins to rotate upward about the pivot. What must be the value of v0 such that the rod comes to a momentary halt in a straight-up orientation, exactly opposite to it initial orientation
The pulse becomes INVERTED upon reflecting off the boundary with the wall. That is, an upward-displaced pulse will reflect off the end and return with a downward displacement. This inversion behavior will always be observed when the end of the medium is fixed, like this wall in this instance. This INVERSION BEHAVIOR can also be observed when the medium is connected to another more heavy or more dense medium. And in this case, when the pulse reaches the end of the medium, a portion of the pulse will reflect off the end and return with an inverted displacement. The heavier medium acts like a fixed end to cause the pulse to be inverted.
Summary: a pulse reaching the end of a medium becomes inverted whenever it either:
i. reflects off a fixed end,
ii. is moving in a less dense medium and reflects off a more dense medium.