Question

if you take snapshots of a standing wave on a string at resonance, there are certain instants when the string is totally flat. what has happened to the energy of the wave at those instants? explain.

Answer 1

The energy of the wave is constant (energy only input to offset friction)

If one examines a single point on the wave starting at a displacement of zero in terms of T/4, period / 4

T/4 - point is at maximum displacement

T/2 - point is at zero displacement

3 T/4 - point is at minimum displacement

T - point back to zero

At T/2 all points on the string are at zero displacement, but points that originally were moving at maximum speed will be moving at maximum speed in the opposite direction