Please Help!

The length of a guitar's strings is 650 mm. What is therefore the wavelength of a wave on any of the strings if the string is free to move?

Me plz i don’t know the charges on each of these

What sort of waves exhibit the doppler effect?

Identify the correct relation showing that the radius r of the orbit of a moon of a given planet can be determined from the radius r of the planet, the acceleration of gravity at the surface of the planet, and the time τ required by the moon to complete one full revolution about the planet. determine the acceleration of gravity at the surface of the planet jupiter knowing that r = 71 492 km and that t= 3.551 days and r= 670.9 × 10^3 km for its moon europa.