Four traveling waves are described by the following equations, where all quantities are measured in SI units and y represents the displacement. I: y = 0.12 cos(3 x + 2 t) II: y = 0.15 sin(6 x - 3 t) III: y = 0.23 cos(3 x + 6 t) IV: y = -0.29 sin(1.5 x - t) Which of these waves have the same speed?

Which pair below describes isotopes of the same element? a) an atom with 6 protons and 8 neutrons - an atom with 8 protons and 6 neutrons b) an atom with 6 protons and 6 neutrons - an atom with 6 protons and 7 neutrons c) an atom with 8 protons and 8 neutrons - an atom with 7 protons and 8 neutrons d) an atom with 7 protons and 6 neutrons - an atom with 6 protons and 6 neutrons