Answer:
B) Periodic Motion
Explanation:
When a pendulum is friction-less, i.e there are no damping forces acting on it, its motion will be periodic, i.e it will bob up and down going from potential energy to kinetic energy and back. Thus, the motion of the pendulum can be best described by the term "period motion", hence choice B.
If however, forces do act on the pendulum, and if they acts as to damp the pendulum, it will oscillate less and less as time goes by, and eventually come to a stop (in the real world this damping force is usually air resistance ). And if the force acts in such a way that it increases the oscillations, the pendulum will swing higher and higher, and the system will go haywire! :)
Lumbar nerves transmit signals that allow us to walk. They are a pivotal part of the human body, and without them we would be immobile. Hope this helps.
Explanation:
It took 
for the sound to reach the 1st wall and at the same time time, the same sound took 
to reach the 2nd wall. Assuming that the sound travels at 343 m/s, then let 
be the distance of the person to the 1st wall and 
be the distance to the 2nd wall. So the distance between the walls X is
