One wave of 1 m amplitude meets another wave of 2 m amplitude. If they are exactly out of phase, what is the magnitude of the new amplitude

1 m

Explanation:

Assuming both waves have the same frequency, and speed, this means that they have the same wavelength.If they are exacty out of phase, one will be at its maximum positive amplitude (crest), while the other will be at its maximum negative amplitude (trough), which means that the magnitude of the new amplitude will be the difference between both amplitudes, i.e., 1 m.If both waves had the same amplitude, the new amplitude would be just zero.

This is what a calorimeter is used for simpler ex, to measure calories in food.