What is the wave speed if the period is 7.0 seconds and the wavelength is 2.1 m?
(Please show how you got it)

Consider an ordinary, helium-filled party balloon with a volume of 2.2 ft3. the lifting force on the balloon due to the outside air is the net resultant of the pressure distribution exerted on the exterior surface of the balloon. using this fact, we can derive archimedes’ principle, namely that the upward force on the balloon is equal to the weight of the air displaced by the balloon. assuming that the balloon is at sea level, where the air density is 0.002377 slug/ft3, calculate the maximum weight that can be lifted by the balloon. note: the molecular weight of air is 28.8 and that of helium is 4.

True or false graphs must include scales that increase by the same amount

Scientific models are based on current knowledge, which can limit their effectiveness when new discoveries are made.