What's heavier a pound of feathers or a pound of stones?

Amira pulls a 3 pound wagon 4 feet. how much work has she done?

If you put a helium-filled balloon in the refrigerator, what will happen?

Which statement best describes the superposition principle? a.) if two in-phase waves arrive simultaneously at a point, their amplitudes add up b.) if two out-of-phase waves arrive simultaneously at a point, their amplitudes add up c.) if two in-phase waves arrive at a point one after another, their amplitudes add up d.) if two out-of-phase waves arrive at a point one after another, their amplitudes adds up