If one single-bladed propeller is turning at 570 rpm and you hear a 2.20 Hz beat when you run the second propeller, what are the two possible frequencies (in rpm) of the second propeller

Why does the equilibrium position of the spring change when a mass is added to the spring? will the mass oscillate around the new equilibrium position of the spring or the previous position without a mass attached to the spring? if the equilibrium position of the spring changes by 20 cm (assuming no initial mass) when a mass is added to the spring with constant 4.9 kg/s^2, what is the mass of the object attached to the spring?