Question

A student makes a simple pendulum by attaching a mass to the free end of a 1.50-meter length of string

Answer 1

-- First, it can never swing to a higher elevation off the floor
than where it was when she let it go.  The higher it is off the
floor, the more potential energy it has, and that's all the energy
she gave it when she lifted it to the height of her chin.

-- Second, it can't even return to THAT height, because during
its swing out and back, it's losing energy by plowing through air. 
So each swing is slightly narrower, and ends slightly lower, than
the one before it.