What phase difference between two otherwise identical traveling waves, moving in the same direction along a stretched string, will result in the combined wave having an amplitude 0.70 times that of the common amplitude of the two combining waves?

What best describes a sonar wave? transverse and electromagnetic transverse and mechanical longitudinal and electromagnetic longitudinal and mechanical

An observer that stands still as the electron moves by him, will observe

Is it possible to use the energy from two atoms colliding to create a clean burning lasting fuel source with a large amount of force? is it also possible to harness that energy from the two atoms colliding to create a clean energy source that will last for years from just two atoms colliding. is there a possibility to control and store that energy for years but slowly let the energy out enough to power cities cheaper and faster.