An echo is heard from a building 0.4 s after you shout "hello." How many feet away is the building if the air temperature is 27°C? (Velocity of sound in air at 0°C is 1087 ft/s)

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?