Which type of heating system includes fans to circulate warm air? (DIsclaimer: Unless you have an explanation on how you got your answer, don't bother awnesering.)

A. Radiant heating
B. Electric baseboard heating
C. Forced-air heating
D. Hot water heating

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?